This protocol prepares chemically competent E coli for plasmid transformation. The competency is high enough for routine cloning but working with libraries may require higher competency. The protocol has worked with every E. coli type I've tried it with. Frozen cells are stable for years at -80, and can be refrozen with minimal effects to their competency. Recommended to get a friend or two to help with aliquoting the bacteria at the end, both so that they stay cool (important) and so that you stay cool (important). Adapted from Promega Cloning Manual Notes and Inoue\/Hanahan protocol, DNA Cloning 1985. With help from Amy Lee, Brandeis (http:\/\/www.bio.brandeis.edu\/leelab\/).