Where is a Kippah worn?
A kippah or yarmulke is a brimless cap, usually made of cloth, worn by male Jews to fulfill the customary requirement held by Orthodox halachic authorities that the head be covered. It is usually worn by men in Orthodox communities at all times, and according to Pewforum.org, up to 82% of the people who wear kippot identify as Orthodox. Most synagogues and Jewish funeral services keep a ready supply of kippot.
There is debate among Halachic authorities as to whether wearing a kippah at all times is required. According to the Rambam, Jewish law dictates that a man is required to cover his head during prayer.
However, according to some authorities, it has since taken on the force of law because it is an act of Kiddush Hashem (lit., "sanctification of the Name", referring to actions which bring honor to God).
The 17th-century authority Rabbi David HaLevi Segal (The "Taz") suggested that the reason was to distinguish Jews from their non-Jewish counterparts, especially while at prayer. He held that nowadays, wearing a kippah is required by halacha (the collective body of Jewish religious laws).