Knowledge-rich contexts express conceptual information for a term. Terminographers need such contexts to construct definitions, and to acquire domain knowledge. This paper summarizes what we have learned about extracting knowledge-rich contexts semi-automatically. First, the concept of a knowledge-rich context is defined, together with its major types and its components. Second, a methodology is described for developing extraction tools that is based on lexical, grammatical and paralinguistic patterns. Third, the most problematic research issues are outlined that must be addressed before semi-automatic knowledge extraction can become a fully mature field.