The most used measuring principles for the determination of the pH are of electrochemical and optical nature. As measuring system glass electrodes and indicator papers are known by every user. Beside this there are further measuring principles for special applications for example the pH determination in tissues, pastes or under extreme process conditions. Furthermore there are methods like NMR for pH-measurement, which will always relegate to a niche existence because of their complex and expensive apparatus. This article gives an overview of the different available methods and discusses potential applications.