This multiple case study develops a model for the creation of radical innovations in knowledge intensive service firms (KISFs). The model distinguishes the phases of idea generation, crystallization and evolution. The underlying processes that constitute the total innovation include learning processes, information processing and soci-political processes. Actors like gate keepers/innovators, boundary spanners and executive knowledge workers play key roles in the innovation process. Management and organizational elements are conditional to the creation of radical innovations with a specific focus on strategic recognition capacity, facilitating external network development, absortive capacity and learning culture. In radical innovation is a strong emphasis on external knowledge acquisiton, conceptualization and experimentation and on personal knwoledge building. Innovation requires continous improvement by professionals.