The bacteriophage M13 has been developed as a cloning vector system to obtain single-stranded DNA templates that are used for the dideoxy chain termination method of sequencing DNA (1 ,2 ). General aspects of bacteriophage M13 as a cloning vector system are reviewed in ref. 3 , and the preparation of foreign DNA fragments (insert DNA) for M13 cloning is described in Chapters 27 and 28 . This chapter describes the preparation of M13 vectors and the ligation of foreign DNA fragments (inserts) into them.