This Halacha is an excerpt from our Sefer
Diminishing in rejoicing:
At the entrance of the month of Menachem Av one diminishes in joy. One is thus not to rejoice at all. [Some however learn that one is merely diminish in joy and does not have to end all joy completely.]
Until when is one to diminish in joy?
Some Poskim say this ruling extends until Rosh Chodesh Elul. Others rule it extends until after the 10th of Av. Others rule it extends until the 15th of Av. Others rule it extends until after Shabbos Nachamu.
Matters of frivolity:
One is to be especially careful during these days not to have conversations of frivolity and lightheartedness.
Jewelry and makeup:
Some Poskim write women are to diminish in makeup and jewelry during the nine days.
 Michaber 551:1; Mishneh Taanis 26b
 M “A 551:1; Elya Raba 551:1; Shulchan Gavoa 551:2; P”M 551 A”A 1; Chayeh Adam 133:9; M”B 551:1; Misgeres Hashulchan; Kaf Hachaim 551:2
Other opinions: Some Poskim rule one is only required to diminish in joy regarding the joyous matters discussed in this chapter. [Mateh Yehuda 551]
 Shaar HaTziyon 551:21 “possibly one only has to diminish his joy and not stop it completely”; Toras Menachem 9:99
 M”A 551:2 in name of Rabbeinu Yerucham regarding avoiding a court case with a gentile; M”B 552:2
 Kaf Hachaim 551:1 and 3; Ben Ish Chaiy Devarim 1; Aruch Hashulchan 551:11; M”B ibid “At the very least until after Tisha B’av”
 Glosses of Chasam Sofer 551; Yifei Laleiv brought in Kaf Hachaim 551:3; Rebbe in Shaareiy Halacha Uminhag 2:225 regarding moving
The reason: As good events occurred on the 15th of Av hence changing the tone of the month.
 Minchas Elazar 3:66 regarding weddings
 Yesod Veshoresh Havoda 11-12
 Ashel Avraham Butchach 551