Patterns, which are based on in-depth practical experience, can be instructing for the design of groupware applications as socio-technical systems. On the basis of a summary of the concept of patterns - as elaborated by the architect Christopher Alexander - its adoptions within computer science are retraced and relationships to the area of groupware are described. General principles for patterns within this domain are formulated and supported by examples from a wide range of experience with knowledge management systems. The analysis reveals that every pattern of a groupware application has to combine the description of social as well as technical structures, and that a single pattern can only be understood in the context of a pattern language. It also shows that such a language has to integrate patterns of socio-technical solutions with measures and procedures for introducing them, and that the language not only has to express one type of directed relationship between the patterns but a variety of different types which have to be deliberately assigned to the patterns.