A siddur is a Jewish prayer book, which contains the Jewish liturgy. Though the basics of the liturgy appear in every siddur, such as the Shema and the Amidah, different communities have developed different standards of prayer. For instance, Sephardic and Ashkenazic communities have slightly different liturgies, as have the contemporary Jewish denominations. As a result, one can find siddurim (plural for siddur) created by and for specific groups, with translations, commentary, layout, and design intended to enhance the prayer of that community.

Siddurim are generally available at the entrance to a synagogue sanctuary, or are kept at each individual seat. In Orthodox communities, many people bring their own siddurim to services with them.