A kippah (Hebrew: כִּיפָּה; pl. kippot), yarmulke, or koppel is a brimless Jewish skullcap, usually made of cloth, traditionally worn by Jewish men to fulfill the customary requirement that the head be covered. It is the most common type of head-covering worn by men in Jewish communities during prayers and by most Orthodox Jewish men at most other times. Among non-Orthodox Jewish individuals, some wear them at most times, while most wear them only during prayer, while attending a synagogue, or at other ceremonies, and others wear them rarely or never.

The term kippah (Hebrew: כיפה) literally means "dome" as the kippah is worn on the head like a dome.

The Yiddish term yarmlke (Yiddish: יאַרמלקע) might be derived from the Polish jarmułka or the Ukrainian yarmulka and perhaps ultimately from the Medieval Latin almutia ("cowl" or "hood"). The word is often associated with the phrase ירא מלכא (yire malka), formed from the Aramaic word for "king" and the Hebrew root ירא, meaning "fear". Keppel or koppel is another Yiddish term for the same thing.

Halachic authorities debate as to whether wearing a kippah at all times is required. According to Maimonides, Jewish law dictates that a man is required to cover his head during prayer.

In non-Orthodox communities, some women also wear kippot, and people have different customs about when to wear a kippah—when eating, praying, studying Jewish texts, or entering a sacred space such as a synagogue or cemetery. The Reform movement historically opposed wearing kippot, but attitudes began to shift in the postwar era, as various social movements encouraged pride in cultural heritage. By the 1970s, the movement had returned to many traditional practices. In the 21st century, wearing a kippah during Torah study and/or prayer has become common and accepted as an option among Reform men and women.

According to several authorities, however, the practice has since taken on the force of law because it is an expression of yir'at Shamayim ("reverence for Heaven"; i.e., respect for God). The 17th-century authority David HaLevi Segal held that the reason is to enforce the Halachic rule to avoid practices unique to non-Jews. Segal reasons that, as Europeans are accustomed to going bareheaded, and their priests insist on officiating with bare heads, this constitutes a uniquely non-Jewish practice. Therefore, he posits that Jews should be prohibited from behaving similarly and rules that wearing a kippah is required by Halacha.

Other Halachic authorities, like the Sephardi posek Chaim Yosef David Azulai, hold that wearing a head covering is a midat hasidut—an additional measure of piety. In a recent responsum, former Sephardic Chief Rabbi of Israel Ovadia Yosef ruled that it should be worn to show affiliation with the religiously observant community.

The Talmud states, "Cover your head in order that the fear of heaven may be upon you." Rabbi Huna ben Joshua never walked four cubits (6.6 feet (2.0 m)) with his head uncovered, saying "because the Divine Presence is always over my head." This was understood by Rabbi Yosef Karo in the Shulchan Arukh as indicating that Jewish men should cover their heads and should not walk more than four cubits bareheaded. Covering one's head, such as by wearing a kippah, is described as "honoring God". The Mishnah Berurah modifies this ruling by adding that the Achronim established a requirement to wear a head covering even when traversing fewer than four cubits, and even when one is standing still, indoors, or outside. Kitzur Shulchan Aruch cites a story from the Talmud (tractate Shabbat 156b) about Rav Nachman bar Yitzchak, who might have become a thief had his mother not saved him from this fate by insisting that he cover his head, which instilled in him the fear of God. In Orthodox communities, boys are encouraged to wear a kippah from a young age in order to ingrain the habit.