Posner's Economic Analysis of Law (1st ed 1973) "brought economic analysis of law to the attention of the general legal academy" (Kornhauser in The Stanford Encyclopedia)
Open access. "This is a pdf version of the ... (6th edition) of Law and Economics by Cooter and Ulen. The ownership of this book has reverted from the publisher to its authors, so [they] are posting it online for everyone freely to read or use as a textbook ...".