This volume begins where volumes 2 and 3 ended. The main theme of the four-volume project is that the law of America’s thirteen colonies differed profoundly when they first were founded, but had developed into a common American law by the time of the Revolution. This fourth volume focuses on what was common to the law of Britain’s thirteen North American colonies in the mid-eighteenth century, although it also takes important differences into account. The first five chapters examine procedural and substantive law in colonies and conclude that, except in North Carolina and northern New York, the legal system functioned effectively in the interests both of Great Britain and of colonial localities. The next three chapters examine changes in law and the constitution beginning with the Zenger case in 1735—changes that ultimately culminated in independence. These chapters show how lawyers became leading figures in what gradually became a revolutionary movement. It also shows how lawyers used legal and constitutional ideology in the interests, sometimes of an economic character, of their clients. The book thereby engages prior scholarship, especially that of Bernard Bailyn and John Phillip Reid, to show how ideas and constitutional values possessed independent causal significance in leading up to the Revolution but also served to protect institutional structures and socioeconomic interests that likewise possessed causal significance.