Involving stakeholders in natural resource management offers both normative and objective benefits, and co-management is a much-studied topic. However, the definition of ‘co-management’ remains vague and incomplete. This thesis develops a definition of co-management that is specific enough to be analytically rigorous and useful, while still maintaining the flexibility necessary to accommodate the diversity of co-management arrangements that can exist. Analysis of the literature on co-management and case studies of collaborative management allowed the development of a matrix containing sixteen variables, each along a spectrum from consultation to co-management, that describe the elements of a co-management arrangement. Testing the matrix on three cases studies labeled as ‘co-management’ revealed the utility of the matrix in testing for the presence or lack thereof of co-management and demonstrated the ways the matrix can be used in the future to compare cases and categorize the level of intensity and completeness of a co-management arrangement.