Tachanun on Erev Yom Kippur:[1]

Tachanun is omitted on Erev Yom Kippur.[2] It is not resumed until the 2^nd day of Cheshvan.[3]

Is Tachanun recited by the Mincha prior to Erev Yom Kippur?[4] Tachanun is recited by Mincha of the 8^th of Tishrei, which is the Mincha prior to Erev Yom Kippur.[5]

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[1] Admur 604:4; Siddur Admur

[2] The reason: Although from the letter of the law Erev Yom Kippur is not a Yom Tov at all [and hence Tachanun should be recited], nevertheless the custom is to treat it like a Yom Tov. [Admur ibid]

[3] Siddur

[4] Admur 604:5; Siddur Admur; M”A 604:1; Levush 131:6; Kaf Hachaim 604:18; 584:74

[5] The reason: As the Yom Tov of Erev Yom Kippur is only accustomed to begin from nightfall even according to those opinions who view the night of Yom Kippur as a Yom Tov and thus decrease in Selichos and eat meat on the night of Erev Yom Kippur. [604:5]

[6] Based on Admur 604:3

[7] Hiskashrus footnote 15

^[8] Tzaruch Iyun on the above ruling in Hiskashrus as the Chabad custom is to never say Selichos during Aseres Yimeiy Teshuvah, hence what proof is there that we consider it a Yom Tov from the night as hold some opinions? To note that in the Siddur Admur writes that Kaparos is followed after Selichos, hence showing that Selichos is said at the night of Erev Yom Kippur. However, it is unclear if it is a normal amount of Selichos or a lesser amount.

[9] See Hiskashrus 948 footnote 48