Tefillin, also known as phylacteries, are a set of small black leather boxes with leather straps containing scrolls of parchment inscribed with verses from the Torah. They are worn by adult Jews during weekday and Sunday morning prayers, except on Shabbat or festivals. The set includes two boxes, one for the head and one for the arm. The arm-tefillah, also known as shel yad, is placed on the upper (non-dominant) arm, and the strap is wrapped around the forelimb, hand, and middle finger. The head-tefillah, also known as shel rosh, is placed between the eyes at the boundary of the forehead and hair, with its straps going around the back of the head, connected at the top of the neck with a special knot, and hanging in front on each side.

Inside the tefillin boxes are handwritten parchments with texts from four passages in the Torah that call upon the Israelites to keep God’s words in mind by “binding them as a sign upon . The word "tefillin" is not found in the Bible, which calls them אות (ot, "sign"), זיכרון (zikaron, "memorial"), or טוטפת (ṭoṭafot) .

Tefillin are worn by men in Orthodox and traditional communities, while some Reform and Conservative (Masorti) communities allow them to be worn by any gender. The use of tefillin is less prominent in Reform and Reconstructionist congregations by both men and women. Tefillin can be purchased at Judaica stores or online. A video tutorial on how to put on tefillin is available on YouTube.