Summary. The kippah (Hebrew; Yiddish yarmulke) is a small head covering worn by Jewish men as a reminder of Hashem’s presence above. The practice originates in Talmudic minhag (custom) rather than explicit Torah commandment (Talmud Kiddushin 31a, Shabbat 156b), but it became universal in Orthodox practice and is increasingly common in Conservative and Reform settings. Styles vary by community: black velvet or felt for Haredi, crocheted kippah srugah for Religious Zionists, suede in Modern Orthodox American settings, large velvet in Hasidic.
The kippah’s origins are in Talmudic minhag. Rav Huna ben Yehoshua (Talmud Bavli, Shabbat 118b) is reported to have said he would never walk four cubits with his head uncovered, because the Shechinah (Divine Presence) is above. Originally an act of particular piety, the covering of the head became standard practice among observant Jews in the medieval period and is treated as obligatory by the Shulchan Aruch (Orach Chaim 2:6, 91:3) for Torah study, prayer, and meals.
The style of kippah marks community affiliation. Among the most common:
Black velvet — Haredi (Ultra-Orthodox), often worn under a hat.
Black felt or suede — Modern Orthodox.
Kippah srugah (crocheted) — Religious Zionist (Dati Leumi) in Israel.
Large black velvet — Hasidic, often combined with a streimel (fur hat) on Shabbat.
White knit with embroidered design — Israeli folk/Sephardic.
Bukharian (large, multi-colored, often square-shaped) — Sephardic / Mizrahi communities, especially Bukharian Jews.
Small clip-on — common in Reform and many Conservative settings.
A standard wardrobe might include a black velvet kippah for formal settings (weddings, funerals), a suede or crocheted everyday kippah, and a special-occasion kippah for Shabbat. Most American Modern Orthodox men wear the same kippah continuously throughout the day.
Where Denominations Diverge
Orthodox: men cover the head continuously; many married women cover their hair (with a sheitel, scarf, or hat) in observance of the laws of tzniut. Conservative: men cover the head during prayer and Torah study, often continuously; women are not required to cover the head, though some egalitarian Conservative women wear a kippah during services. Reform: head covering is optional; traditional Reform actively discouraged it as “Eastern”; current Reform commonly affirms it as a meaningful practice. Reconstructionist: optional and increasingly common.
Sources
Talmud Bavli, Shabbat 118b; Kiddushin 31a; Shabbat 156b.
Shulchan Aruch, Orach Chaim 2:6, 91:3.
Mishnah Berurah on Orach Chaim 2.
Further Reading
Eric Silverman, A Cultural History of Jewish Dress.
Donin, To Be a Jew, chapter on garments.