The increasing prevalence of co-occurring multiple chronic conditions in an aging population has influenced the debate on complexity in chronic care and nowadays provides an impetus to the reform of numerous health systems. This article presents a theoretical lens for understanding the complexity of chronic care based on research and debate conducted in the context of multiple quality improvement programs over the last five years in Belgium and The Netherlands. We consider four major components of complexity in chronic care against a background of complex adaptive systems: (1) case (patient) complexity; (2) care complexity; (3) quality assessment complexity; and (4) health systems complexity. Each of these components represents a range of elements that contribute to the picture of complexity in chronic care. We emphasize that planning for chronic care requires equal attention to the complexity of all four components. It also requires multifaceted interventions and implementation strategies that target improvements in multiple outcomes related to the structural, process, and outcome components of care. Further empirical research is needed to assess the validity of our complexity framework in the health-care environment.