The purpose of criminal procedure in a liberal and democratic society is to gather evidence of crimes, to identify and punish the truly guilty with certainty and without error, and at the same time to exonerate the innocent as early as possible, with the least possible infringement of constitutional freedom. However, the arguments and controversies in the study of the law of criminal procedure are often too much influenced by ideological and dogmatic concepts such as “adversarial system” and “inquisitorial system.” This chapter examines the history of criminal procedure, both “adversarial” and “inquisitorial,” and the current state of criminal justice in the United States from an empirical and utilitarian perspective. On this basis, it explores solutions to the problems we face today and suggests important general principles that should be followed in legislating and interpreting the law of criminal procedure.