Collaborative problem solving (ColPS) proficiency was developed as a new assessment for the Programme for International Student Assessment (PISA) in the 2015 international evaluation of student skills and knowledge. The assessment framework defined by the PISA ColPS 2015 expert group crossed three major collaboration processes with four problem solving processes that were adopted from the PISA 2012 individual problem solving assessment to form a matrix of 12 specific skills. The three major collaboration processes are (1) establishing and maintaining shared understanding; (2) taking appropriate action; and (3) establishing and maintaining team organization. The four problem solving processes are exploring and understanding the problem, representing and formulating the problem, planning and executing strategies, and monitoring and reflecting on the problem-solving activities. This article discusses how the problem-solving dimension was integrated with the collaboration dimension. We also discuss how computer agents were involved in the PISA ColPS 2015 assessment in order to ensure a satisfactory assessment of collaborative problem solving. Examples of the use of agents to assess ColPS are provided in the context of a released PISA item and a project conducted in Taiwan.