This chapter examines the idea of separating distinct governmental functions into at least three branches (horizontal separation) as a means to safeguard individual liberty. The three branches of government have different functions: the legislature legislates, the executive branch executes the laws, and the judiciary administers justice. This corresponds to the functional distribution of essential governmental tasks and competences. The chapter explores how governments based on separated (or at least divided) powers work, in a perpetual balancing exercise as a result of the operation of checks and balances. Finally, it discusses independent agencies that are now routinely added to the old constitutional mix of powers and the problem of outsourcing public powers to private actors.