The Comprehensive Approach (CA) to crisis management operations is an essential element in NATO’s transformation in modern operations. At the Bucharest Summit in April 2008, Allied leaders endorsed an Action Plan for the development and implementation of NATO’s contribution to a Comprehensive Approach. This was endorsed in later summits and meetings, focusing on how to improve the coherent application of the comprehensive set of crisis management instruments and better cooperate with other actors in order to complement and mutually reinforce each others’ efforts. The NATO HFM 204 Research Workshop (Oct, 2010) on ‘Collaboration in a Comprehensive Approach to Operations’ (Effective Collaboration in Joint, Multinational, Multiagency Teams and Staffs) brought together the latest research in these areas, integrating diverse disciplines, and combining those insights with actual operational experiences. The workshop identified key issues in the operational context that have yet to be addressed by the scientific community, and developed recommendations to further focus research efforts. Collaboration is a hard problem. A list of these problems includes: Diversity of cultures, objectives, motives, principles, and time horizons is the rule; there is often no unity of command and national independence is critical; cultural differences, social identities, stereotypes, and prejudices complicate interoperability; well developed competencies, collaboration skills and cultural awareness are needed to operate in these diverse conditions; personnel rotations cause lack of knowledge of partners and also loss of trust between partners. Theories related to forming, developing and sustaining ad hoc collaborations - Trust development in ad hoc collectives - Mission preparation/training for Comprehensive Approach - Multi-team systems - Competencies of senior and junior leadership - Metrics of collaboration / cohesion at the larger unit and meso levels - Data collection in the field with non-obtrusive measurement techniques - Lessons learned from e.g. PRTs and civil bodies, e.g. EU.