A kippah (meaning "dome"), also known as a yarmulke or skullcap, is worn by religiously observant Jewish men as a sign of respect and reverence for God. In traditional Jewish communities, men wear a kippah at all times, while others only wear one when they pray, study Torah, say a blessing, or enter a synagogue.
The practice of wearing a kippah originated in biblical times, when priests were taught to cover their heads in the Temple as a reminder of what’s above -- namely, God. Wearing one today reminds Jewish men of their submission to this higher authority.
In Israel, the style of one’s kippah is often a sign of a certain political or religious affiliation. For example, classic orthodox men usually wear large, smooth, black kippot (plural of kippah) shaped like a bowl. Men in modern orthodox, conservative, and reform communities often wear leather or crocheted kippot (like the one pictured above).