Preparation of pure bacteriophage DNA used to rely on using CsCl gradients to give high purity or methods that yielded DNA that was either of low recovery or subject to significant genomic contamination. Recently though, new methods have come along that allow the purification of DNA from plate lysates that are not only capable of high yield but also, for all intents and purposes, free of genomic contamination (i.e. no visible genomic contamination on restriction analysis or when used for bacteriophage sequencing). This protocol that form the basis of this short section can be used to prepare bacteriophage DNA from one or two 9 cm L-agar plates. For these preps, the use of agarose in the top agar is recommended to avoid any restriction inhibitors that may be present in some agar preparations.