Separation of powers is one of the fundamental principles underlying the U.S. system of government. The Constitution seeks to prevent abuses of power by separating government functions into independent branches - legislative, executive, and judicial. However, this system is sometimes inefficient. Separation of Powers, the first book in the Understanding Constitutional Principles Series, examines the crucial elements of this constitutional concept. The first half of the book explains the separation of powers doctrine, the core functions of the branches and the struggles between the branches. The second half of the book consists of approximately 75 primary source documents, with unique explanatory headnotes, exploring various historical and philosophical approaches to separation of powers as well as governmental documents from the legislative, executive, and judicial branches.