The Trinity approach is an attempt to provide methodological support for knowledge brokerage activities. Knowledge brokers are a type of knowledge managers dedicated to problem solving processes in knowledge-intensive multi-actor problem contexts. Trinity was originally designed for environmental problems. The approach however is generic, and may be used to support multi-actor problem solving processes in other domains as well. In this paper, some of the foundations of Trinity are sketched. Parts of the Trinity modelling language are presented. The use of Trinity is illustrated by means of parts of a small case study, concerning reduction of the emission of air pollution, that was conducted for the Dutch government. The paper ends with a short discussion of Trinity from a knowledge management point of view.