The focus of this paper is to introduce a comprehensive model for assessing and improving the maturity of Collaboration Engineering (CE) processes. The model is targeted at introducing evolving CE processes within an organization and across organizational boundaries. The capability assessment dimension of the model is derived from the ISO/IEC 15504 assessment approach. The two-dimensional assessment model addresses the phases of the CE approach as well as their associated maturity levels. The CE phases are defined in terms of their purposes, objectives, and base practices. The assessment model can be used to benchmark and perform repeated analysis, thus supporting continuous improvement of collaboration engineering processes.