The inherent ambiguity and complexity of natural languages often leads to understanding and translating difficulties. Controlled languages address this problem by defining guidelines for and restrictions on the language used to author texts. Through the use of CL, texts become easier to read, understand and translate. CLs are typically applied to different types of technical documentation. The second section addresses the issue of how CL is applied to a particular writing process through document checking and correction. In the third section, various characteristics of CL are discussed, as it is used in combination with machine translation. A discussion of evaluation methods is presented in section 4. A detailed case study of a particular CL system (KANT) is presented in section 5. Section 6 concludes with a summary plus a discussion of future trends in CL research and development.