The Rebbe's halachic responses and clarifications, and his guidance on who decides halachah and how:
Who decides. Practical rulings belong only to qualified rabbis — not to a scientific institute or any other body, however expert (IK 9866). In a court case such as the mechitzah question, rely on the unified position of Orthodox rabbinic authority rather than on arguments that invite challenge (IK 5521). The standing of a heter issued by local rabbis should be clarified with them, and their authority respected (IK 7976); one may not testify about a person's fitness as a rabbi without real knowledge (IK 8481). For complex questions, consult rabbinic authorities (IK 9088). Work to save souls needs no one's approval — do it in the most effective way (IK 2431). On the Yerushalmi's reading of following rabbinic authority, see IK 1742; on the authority of rabbinic decrees, IK 3386.
Rejecting mistaken rulings. Opinions permitting the exhumation of graves must be firmly rejected, especially when falsely grounded in mystical teachings (IK 4285, 4424). A Haggadah suggesting a fifth cup at the Seder contradicts the Shulchan Aruch and accepted authorities and should not be published that way (IK 7961). On a public controversy over kosher meat, see IK 965; on questionable sources of support such as Israeli ships sailing on Shabbos, IK 4535.
Halachah and Chassidus. Likkutei Torah is not a book of halachic rulings; Chassidus discusses every opinion, including those not followed in practice (IK 2785). What the Zohar says about Kohanim without a wife is a measure of piety, not a strict prohibition (IK 576).
Disputes. Avoiding a dispute comes first — for example, when leading prayers in a different nusach from the congregation's (IK 5165).
Specific halachic discussions. Whether one is judged only on Rosh Hashanah (IK 144); Hallel at the Korban Pesach and the two cooked dishes (IK 308); a get and its procedures (IK 547); false testimony even without financial loss (IK 2806); the Rambam on the requirements of a Torah scholar (IK 161); the Torah reading (IK 2502); the Manhattan eruv (IK 2786, 2936); strengthening halachic foundations through works such as Otzar HaPoskim (IK 9289); comments on scholarly disagreements (IK 551, 5604).
See also: Halachah and custom – Asking a Rav, stringency and halachic questions; Halachah and custom – Customs and minhagim; Shabbos and holidays – Eruv.