This paper, by means of original Bedouin documents relating to matters of personal status, attempts to disclose interaction between custom and sharī'a and to illuminate some of the mechanisms tending to complete the islamization of a tribal society in process of sedentarization. The Bedouin dealt with here are a group of tribes in the Jerusalem-Bethlehem region: al-Sawāhira (c. 6,000 persons now) east of Jerusalem, al-'Ubaydiyya (c. 5,500) east of Bayt Saḥūr, the 13 al-Ta'āmira tribes (c. 20,000) extending over a sector east of Bayt Saḥūr in the north to Bayt Fajjār in the south, and al-Rashā'ida (c. 500) south-east of Taqū'a. Most of these tribes originate from Ḥijaz and Najd. They appeared in the region in small groups from the sixteenth century and in time developed into tribes, while absorbing local fallāḥs. Their main numerical increase took place in the twentieth century.