Shabbos Mevarchim Hachodesh:
A. Blessing the new month:
[It is a vintage custom of previous generations that] on the Shabbos prior to Rosh Chodesh we bless the new month [that it should be a month filled with good tidings for the Jewish people]. [The blessing takes place after the reading of the Haftorah [and Yikum Purkan], prior to Ashrei. This Shabbos is cordially known as Shabbos Mevarchim.]
The month of Av: It is customary to bless the month of Av as is done prior to every other month. However, in some communities, the custom is to refrain from blessing the month of Av being it is a month of bad occurrences.
Rosh Chodesh that falls on Shabbos: When Rosh Chodesh falls on Shabbos the blessing of Mevarchim Hachodesh takes place the previous Shabbos.
Sparks of Chassidus
Shabbos Mevarchim Tishrei-Hashem blesses this month:
On the Shabbos before Rosh Hashanah, which is the last Shabbos of the month of Elul, we read the passage in the Torah which begins נצבים אתם. These words are G-d’s blessing to the Jewish people. The Rebbe Rayatz records the following statement from his father the Rebbe Rashab: When I was a child I asked my father, the Rebbe Maharash: Why do we not bless the month of Tishrei as we bless the other months? The Rebbe Maharash replied that when he was a child he had asked the same question to his father the Tzemach Tzedek, who in turn said that when he was a child he asked this question to his grandfather the Alter Rebbe. The Alter Rebbe replied that he heard the following teaching in Mezritch from his master, the Maggid, who had received it from his master, the Baal Shem Tov: The seventh month [i.e. Tishrei], which is the first of the months of the year, is blessed by G-d Himself on Shabbos Mevarchim, which is the last Shabbos of the month of Elul. By virtue of this blessing the Jews are empowered to bless the other months eleven times a year. This is the content of G-d’s blessing: “Atem Nitzavim Hayom” [i.e. You are standing this day]. The word היום [i.e. this day] refers to Rosh Hashanah, which is the Day of Judgment. The phrase Atem Nitzavim implies not only that the Jewish people are standing, but furthermore, that on this day “you are sustained in your firm stance” which means that you are acquitted in your trial.
B. Announcing the Molad:
It is proper for one to know the Molad prior to reciting the blessing over the new month. [It is therefore customary in all Shuls for the Chazan or Gabaiy to announce the Molad prior to reciting the Birchas Hachodesh. If one did not hear the Molad or does not know its date, he is to continue as usual with the Birchas Hachodesh.]
D. The Nussach of Birchas Hachodesh:
Yehi Ratzon: Some have the custom to recite a prayer of Yehi Ratzon, which includes requests for all matters of blessing, prior to the recital of the day of Rosh Chodesh. This is not the Chabad custom, and rather we begin with the words “Mi Sheasa Nissim”.
Repeating after the Chazan: The congregation is to repeat the dates of the upcoming month after the recital of the Chazan, and is not to rely on merely hearing the dates from the Chazan.
When Rosh Chodesh falls on Shabbos-Sunday: When Rosh Chodesh falls on Shabbos-Sunday the Nussach recited by the dates of the new month is “Hashabbos Kodesh Ulimacharaso Beyom Harishon”. One however does not say Limacharaso by a two day Rosh Chodesh that falls in the same week.
Leap year: By the Shabbos before the month of Adar in a leap year one says “Adar Rishon” by the first Adar and “Adar Sheiyni” by the second Adar.
E. Holding the Sefer Torah:
The custom is for the Chazan to hold the Sefer Torah upon reciting Birchas Hachodesh. [When there are two Sifrei Torah’s, the Chazan is to take the Sefer of Maftir.]
F. Av Harachamim:
Av Harachamim is not recited on Shabbos Mevarchim.
Shabbos Mevarchim Iyar: On Shabbos Mivarchim Iyar, Av Harachamim is omitted just like every other Shabbos Mevarchim.
Shabbos Mevarchim Sivan: On Shabbos Mivarchim Sivan, Av Harachamim is recited.
Shabbos Mevarchim Tishrei: On Shabbos Mevarchim Tishrei, being that we do not bless the new month, one recites the paragraph of Av Harachamim prior to Musaf.
Tehillim Shabbos Mevarchim:
The Rebbe Rayatz instituted that the entire Tehillim be recited prior to Shacharis on Shabbos Mevarchim. Following the Seder of Shabbos Mevarchim is extremely pertinent to the public, and is a great and lofty Mitzvah which brings an abundance of blessing in physical and spiritual matters. The saying of Tehillim daily after Davening and on Shabbos Mevarchim has future effects on one’s children and grandchildren.
With a Minyan: The institution was for the Tehillim to be recited specifically together as a congregation, and not each person individually.
For all Chassidim: The above institution applies for all Chassidim, even those that spend their time learning Chassidus and Davening in length. They are nevertheless to say the Tehillim specifically with the congregation.
For all Jews: This institution is relevant for all sects of Jewry and not just for Chabad Chassidim. The Rebbe Rayatz placed due effort to bring other groups to recite the Tehillim on Shabbos Mevarchim. The Rebbe once stated “When Moshiach comes he will not accept any excuses, and he will ask how many Jews did you influence to participate in the Tehillim of Shabbos Mevarchim.” This institution is to be publicized to all Jews, in the name of the Rebbe Rayatz.
Kaddish: If there is a Chiyuv present [an Avel within 11 months of a parents passing or one who has a Yartzite of a parent that day] then Kaddish is to be recited after each Sefer. If a Chiyuv is not present, then Kaddish is not to be recited between each Sefer, although at the conclusion of the entire Tehillim, Kaddish is to be recited by one who does not have any parents.
Yehi Ratzon: In the event that Kaddish is being recited between each Sefer, the Yehi Ratzon for each Sefer is to be recited prior to each Kaddish. At the very least, it is to be recited by the person saying the Kaddish. Today, the Yehi Ratzon is customarily recited by the entire congregation, however some are accustomed not to say it, unless they are saying Kaddish or are leading the Tehillim. The Rebbe was not accustomed to recite the Yehi Ratzon after each Sefer, but rather only once after the entire Tehillim. In the event that there is no Chiyuv present and Kaddish is not being recited between each Sefer, it is implied that one does not recite the Yehi Ratzon between each Sefer.
Verses before and after the Tehillim: It is not customary to recite the verses of Lechu Neranena printed prior the start of the Tehillim, nor the verses printed after the completion of the Tehillim.
Shabbos Mevarchim Tishrei: The entire book of Tehillim is recited before Shacharis just as on any other Shabbos Mevarchim.
Does the recital of Tehillim on Shabbos Mevarchim push off Davening with a Minyan?
- On Shabbos Mevarchim, is one to finish the recital of Tehillim before Davening even if this will cause him to be unable to Daven with the Minyan?
The age old custom of saying the entire Tehillim prior to Davening does not take priority over Davening with a Minyan. This applies likewise to the Tehillim recited prior to Davening on Shabbos Mevarchim, that it certainly does not take priority to Davening with the Minyan. One is thus to be very careful that if he arrives to Shul while they are up to Davening, that he not make the secondary primary and primary secondary [and say Tehillim while they are Davening].
When is one to recite the Tehillim if he is unable to complete it before Shacharis?
It may be said after Shacharis, after Mincha, and anytime throughout the day until night time. It is not to be recited on Motzei Shabbos until after midnight. If necessary, it may even be completed on Sunday, or even the next Shabbos. One may also begin saying it on Shabbos morning prior to the start of the Minyan. It is questionable whether it may be said on Friday night before midnight.
Mamar Chassidus before Davening:
After the completion of the Tehillim, the congregation is to study for approximately one hour a Chassidic discourse that is understood to all.
Farbrengen of Shabbos Mevarchim:
After Davening on Shabbos Mevarchim, the congregation is to hold a Chassidic gathering.
When: The gathering is to take place in accordance to the time that best fits the community, and for this purpose, can be delayed until the third meal or Melaveh Malka. During the summer months the Farbrengen is to take place during the day of Shabbos while during the winter months [it can be arranged to take place] on Motzei Shabbos.
Eating the Shabbos meal with one’s family: The Shabbos day meal with one’s family is not to be exchanged for the Shabbos Mevarchim farbrengen. The Farbrengen is to be arranged in a way that the participants can return home to their families and join them for the Shabbos meal.
Sharing the content of the talks with one’s family: Upon returning home, one is to share with one’s family the content that was spoken by the Farbrengen, and hence continue the Farbrengen with his family at home.
Women: It is proper that also the women and girls establish a Chassidic gathering amongst themselves on Shabbos Mevarchim, or on Motzei Shabbos.
Children: It is proper for even little children of three years of age to attend Farbrengens in order so they squeeze themselves between the Chassidim [and learn from them].
 M”A 417/1; Abudarham Seder Rosh Chodesh [regarding announcing the days of Rosh Chodesh]; Machzor Vitri p. 173; Kol Bo 37; Yireim 259; Or Zarua 2/453; Shivlei Haleket 170; Rokeiach 53; Kneses Hagedola 284; Siddur Yaavetz; M”B 417/1; Kaf Hachaim 417/1; See also Yerushalmi Sanhedrin 5/3; Tosefes Reiemim on Yireim ibid; Aruch Hashulchan 417/6; Pnei Moshe on Yerushalmi ibid; Likkutei Sichos 9/184 footnote 1
 M”B ibid; Yireim ibid “Takanas Harishonim”
 This blessing on Shabbos affects the entire week to follow, which includes Rosh Chodesh, which in turn effects the entire month. [See Likkutei Sichos 19 p. 160 footnote 2]
 The reason: In previous times, when the month was sanctified based on testimony of the witnesses, after the testimony was accepted the Beis Din would say a blessing over wine and then recite a blessing to Hashem, as well as a prayer. [Miseches Sofrim 19/9] Seemingly, from this custom evolved the current custom to recite Birchas Hachodesh every Shabbos prior to Rosh Chodesh. [See Shaar Hakolel 26/7] Nevertheless, this recital of Birchas Hachodesh is not the actual sanctification of the new month as was done in previous times. [Yireim brought in M”A 407/1] The reason for this is because this sanctification was done by Hillel who created the calendar after the destruction, and he sanctified the months of all the future years. [Machatzis Hashekel ibid; Kaf Hachaim 407/7] In additional purpose of blessing the month is in order to publicize the dates of Rosh Chodesh to the congregation which gathers on Shabbos. [Shiveli Haleket ibid; Levush 421/1; Yoreim ibid]
 Abudarham; Siddur Admur
 Magen Avraham 417/1; Levush 421/1; 581/1; Kneses Hagedola 284; Minhagim Tirana; Mateh Efraim 581/47
 The reason: The reason for this is because the verse in Psalms states on Rosh Chodesh “Bikese Leyom Chageinu” which implies that Rosh Hashanah is to be concealed. Hence we do not announce the date of Rosh Chodesh which is the date of Rosh Hashanah. [Magen Avraham ibid] The reason we desire to conceal Rosh Hashanah is in order to confuse the Satan and prevent him from prosecuting against us on that day. [Levush 421/1]. The Rebbe explains that the Satan is confused by the lack of mentioning Rosh Chodesh as he now becomes even more convinced that the Jews are positive that their judgment has been sealed for good, and it is for this reason that they are not doing the Mitzvah of Rosh Chodesh. This hence weakens the Satan’s prosecution, being that he suspects that perhaps the judgment has already been secured. It also diminishes the Satan’s personal prosecutions, as he sees that they are lacking the merit of Rosh Chodesh and hence a strong prosecution is not that necessary. Nevertheless, in truth, the above explanation does not suffice to justify annulling a custom of Jewry, as practically we are now lacking the Avoda of Rosh Chodesh. Thus, in truth, the intent of not mentioning Rosh Chodesh is to arouse one in Teshuvah, so we become broken over the Mitzvah that was removed from us. It is this Teshuvah that is done due to feeling broken hearted that capsizes the Satan’s prosecution.[Likkutei Sichos 24 printed in Shaar Hamoadim Rosh Hashanah 5] Alternatively, the reason is because everyone is aware that on Rosh Hashanah is Rosh Chodesh, and hence there is no need to announce the dates in Shul. [Shaar Hatziyon 417/4]
The Chassidic reason: See Sparks of Chassidus!
 Mordechai Moed Katan 934; Chida in Ledavid Emes 24/1; Poskim brought in Kaf Hachaim 417/5; Shaar Efraim 10/35; Siddur Yaavetz; Aruch Hashulchan 417/9; Chabad custom
The reason: As this month needs our blessing even more than other months as it is a month of negative occurrences. [Kaf Hachaim ibid]
 Custom brought in M”A 417/1; Kneses Hagedola 284; M”B 417/1; Mordechai Moed Katan 934 in name of Tosefes Shabbos
The reason: As it is a month of negative occurrences and is hence not to be blessed. [Machatzis Hashekel; M”B ibid]
 Maharil R”H; Kaf Hachaim 417/6
 Hayom Yom 25th Elul; Sefer Haminhagim p. 115 [English]
 Siddur Admur; Siddur Shlah; Shaareiy Efraim 10/37 “Some are accustomed”; Kaf Hachaim 417/8; Karnos Tzadik 3/93; See Shaar Hakolel 26/7; Aruch Hashulchan 417/8; Yaskil Avdi 7/27-4
Start of custom: The custom of knowing the Molad prior to Kiddush Hachodesh is first brought in the Siddur Shaar Hashamayim of the Shlah and is likewise recorded by Admur in his Siddur.
Other opinions: Some write it is improper to announce the Molad to the community. This is hinted to in the verse “Vein Esther Magedes Moladita”. [Shaareiy Efraim 10/37] The Sefaradi custom is not to announce it.
 The exact time that the new moon will appear.
 The reason: The reason for this custom is because in times that the month was sanctified based on testimony the witness would give the testimony of the moon and then a blessing over the month was recited. [See Miseches Sofrim 19/9] Thus, likewise today, we first recite the Molad, which is similar to the testimony, and then bless the month. [Shaar Hakolel ibid] Alternatively, the reason is because the entire meaning of the word Chodesh is from the renewal of the new moon and it is we hence mention it during this time. [Shaareiy Efraim ibid] The Shaareiy Rachamim [in Shaareiy Efraim] 10/47 writes that the saying of the Molad during this time is auspicious for the Tikkun of Pgam Habris.
 So is the custom of Anash; See Shaarei Efraim 10/36
 Shaareiy Efraim 10/37
 M”A 417/1
 The reason: During the times when the sanctification of the new month was done based on testimony of witnesses before the court in Jerusalem, the sanctification was done in a standing position. For this reason it is customary today to stand during Kiddush Hachodesh, despite the fact that it is not similar at all to the sanctification of the month in previous times. [M”A ibid] Some explain this to mean that the congregation would stand while the judges [who were sitting] would sanctify the moon. [Igros Moshe 142; See Likkut Dinei R.C. 1 footnote 13]
Other Opinions: Some Poskim question this premises that the Kiddush Hachodesh was done standing and learn that in truth it was done sitting. [Hagahos Reb Akiva Eger ibid; Daas Torah 417; See Rosh Hashanah 25b; See Igros Moshe ibid]
 See Abudarham Seder Rosh Chodesh; Siddur Yaavetz; Kaf Hachaim 417/2-3 for the different dialects of this Yehi Ratzon.
Tikkun for Zera Levatala: In Siddur Yaavetz a prayer of Yehi Ratzon for waste of seed is brought prior to the blessing of the month. The Shaareiy
Rachamim [in Shaareiy Efraim] 10/47 writes that this is an auspicious time for the Tikkun of this sin.
Prayer for Torah scholars: In the Abudarham and Shalmei Chagiga p. 219 it mentions that they would pray for the Sages prior to Birchas Hachodesh, as it was the Sages of the Sanhedrin who would sanctify the month. Perhaps this is similar to our prayer of Yekum Purkan that we say every Shabbos.
 Siddur Admur omits the Yehi Ratzon; See also Aruch Hashulchan 417/9 who questions its recital on Shabbos; Minhagei Chasam Sofer 5/24
 Kaf Hachaim 417/9
 Hiskashrus 672 in name of Rav Shusterman who was the Chazan for Musaf by the Rebbe’s Minyan; See Likkueti Sichos 20/555 that the Rebbe directed the asker to ask Chazanaim that have Mesorah in this matter.
 Shach Y.D. 220/17 in name of Maharil R”H brought in M”A 427/1; Chida in Ledavid Emes 24/2; Machatzis Hashekel ibid; Kaf Hachaim 417/6; Darkei Chaim Veshalom 476; Rebbe in Sefer Hasichos 1992 Parshas Mishpatim
Other customs: Some are accustomed to recite just “Adar” by the first Adar and by the second Adar they say “Adar Sheiyni”. [M”A 427/1 in name of Maaglei Tzedek, based on Rama 427/1; Kneses Hagedola 284/4; Ledavid Emes ibid]
 Shaarei Efraim 10/36; Machatzis Hashekel 96/1; Ketzos Hashulchan 83 footnote 10; See Igros Moshe 142
 Shaareiy Efraim 10/41; Piskeiy Teshuvah 150/4
Bedieved: If the Chazan accidently took the first scroll, it is not to be switched for the second scroll due to worry of Pegam. [Shaareiy Efraim ibid]
 Siddur Admur; Admur 284/14; Rama 284/7; Sefer Haminhagim Tirana
 The reason: The prayer of Av Harachamim was established in memory of the Jews murdered in Ashkenaz during the period of the Crusades. [See Shaar Hakolel 26/8] It is hence omitted on Shabbos during times in which we have extra Simcha.
 Implication of Admur in Siddur who omits Iyar; Admur 429/8 in parentheses; Piskei Hasdiddur; See Beir Hagoleh 284 in name of Maharshal; Siddur Kol Yaakov
Ruling of Admur in Shulchan Aruch and other Poskim: Av Harachamim is to be recited on Shabbos Mevarchim Rosh Chodesh Iyar due to the terrible decrees that occurred in this month. [Admur 284/14; implication of Rama ibid; M”A 284/8]
 284/14; Rama 284/7; Admur in Siddur
 The reason: As terrible decrees occurred during this time period of Sefira and hence we recite this prayer. [Admur ibid; See Hisvadyos 1983 p. 1448] This refers to the decrees of the year 4856/1096, the first Crusades. [Machatzis Hashekel 284]
 Mateh Efraim 581/47; Shaareiy Efraim 10/35; Toras Menachem 1990 4/299 [Sichas Netzavim Vayeilech; brought in Shaareiy Halacha Uminhag 5/68; Shulchan Menachem 3/75]
 The reason: Although on a regular Shabbos Mivarchim the paragraph of Av Harachamim is omitted, nevertheless since on this Shabbos the month is not verbally blessed in Shul therefore one is to recite this paragraph.
 Luach Hayom Yom 26th Kisleiv; Igros Kodesh Rayatz 3/422
 See however Igros Kodesh Rayatz 3/578 that the Rebbe suggested that the Tehillim can be said as a congregation either before Shacharis, or between Mincha and Maariv, in accordance to whatever is best for the Minyan.
 This institution began with a letter written by the Rebbe Rayatz to the general Anash dated on the 15th of Menachem Av 1935 [printed in Igros Kodesh Rayatz 3/422] The background behind the initiation of this institution was as follows: A Chabad Chassid by the name of Chaim David Lein, a Shochet from the town of Nevel, sent a letter to the Rebbe Rayatz in the summer of 1935, suggesting that all Anash recite the entire Tehillim before Davening every Shabbos. The Rebbe Rayatz replied that it is a good suggestion, although should not be done every Shabbos, but specifically on Shabbos Mevarchim. In a letter written in honor of the 13th of Tamuz, the Rebbe Rayatz wrote “I am very pleased to hear of the public recital of Tehillim on every Shabbos Mevarchim, as suggested to me by my colleague and friend, Chaim Dovid Shuv.” Approximately one month later, the Rebbe Rayatz sent out the official letter to all Anash, publicizing the institution.
 Igros Kodesh Rayatz 3/471
 Hayom Yom 25th Shevat
 Hayom Yom ibid; Igros Kodesh Rayatz 3/578; Sichas Shabbos Bereishis 1961; Toras Menachem 21/115
 Sichas Shabbos Bereishis 1961
 See Igros Kodesh Rayatz 3/578 for a letter of the Rebbe Rayatz to the Kupshitzner Rebbe
 Sichas Pekudei 1967
 Igros Kodesh 5/33
 Sefer Haminhagim p. 59 [English]; Igros Kodesh 10/304 [printed in end of Kovetz Michtavim in Tehillim Oholei Yosef Yitzchak] based on a directive of the Rebbe Rayatz
 Igros Kodesh 10/304 [printed in end of Kovetz Michtavim in Tehillim Oholei Yosef Yitzchak]; Sefer Haminhagim p. 59 [English] footnote 237
 In a written response from Rabbi Leibal Groner he stated that one does not say the Yehi Ratzon unless he is leading the Tehillim or is saying the Kaddish afterwards.
 Hiskashrus 483
 Hiskashrus ibid
 See Shaareiy Halacha Uminhag 5/13 “I did not hear anything on this issue and hence I cannot give a directive on this issue”; See Hiskashrus 445 and 484
 Sefer Haminhagim p. 115 [English Edition]; Takanos of Rebbe Rayatz printed in Otzer Minhagei Chabad 81
 Introduction to Tehillim Ohel Yosef Yitzchak [I have not found this section in the Shlah Hakadosh]
 Kovetz Zalman Shimon p. 30; Hiskashrus 942 footnote 1
 Introduction to Tehillim Ohel Yosef Yitzchak [I have not found this section in the Shlah Hakadosh]; See also Likkutei Yekarim 25 that the Maggid stated one is not to say Tehillim before Davening in a way that will come in the expense of Davening.; In Sefer Devek Tov this is brought in the name of the Baal Shem Tov.
The reason: As the main reason of Tehillim is to fight off the prosecuting angels, and this also is accomplished through Pesukei Dezimra. [ibid]
 Letter printed in Shulchan Menachem 2/192 [throughout the day]; Heichal Menachem 3/266 based on a Yechidus with Rav Y. K., told over by Rav Levi Goldstein [after Mincha and on Sunday, but not at night]; Hiskashrus
 See Hiskashrus 942 footnote 1 an answer of the Rebbe for it to be recited between the Sichos of the Farbrengen.
 Heichal Menachem 3/266
 See Koveitz Hearos Oholei Torah 22/14 and 171/14
 See Kuntres Dinei Uminhagei Rosh Chodesh p. 7 that the Rebbe once said it may be recited “throughout the 24 hours of Shabbos” if one is unable to complete it otherwise.
 As one is not to say Tehillim at night. [Beir Heiytiv 238/2; Chaim Sheal 24] However some Poskim rule that this law does not apply on Friday night. [Ben Ish Chaiy Pekudei 7; Kaf Hachaim 237/9] On the other hand see Sefer Haminhagim p. 41 [English] that does not list Shabbos and Yom Tov as one of the days that permit Tehillim to be said at night. Vetzaruch Iyun. See previous footnote!
 Hayom Yom 26th Kisleiv
 Igros Kodesh Rayatz 3/423 and 430; Toras Menachem 21/115
 See Igros Kodesh Rayatz 11/261
 Igros Kodesh Rayatz 4/388
 Likkutei Sichos 16/523
 Likkutei Sichos ibid
 Likkutei Sichos ibid; See Igros Kodesh Rayatz 4/361
 Toras Menachem, vol. 5, p. 180