The article explores the concept of the presumption of innocence in the legal system. It discusses how this principle balances the need for efficient law enforcement with protecting individual rights. The study clarifies the theoretical function of the presumption of innocence and its importance in ensuring a fair trial. It also outlines the specific rules and criteria that govern its application in practice. The research is divided into three parts, examining the systematic importance of the presumption in the legal process, its definition by European bodies, and its application in Sweden. The goal is to provide a clear understanding of the requirements and functions of the presumption of innocence in the legal system.