BACKGROUND: Complex interventions in health care are characterized by multiple interacting components as well as by numerous nonlinear interactions with the social systems within which they are being implemented. The process of developing, evaluating and implementing complex interventions is therefore challenging. Established guidance such as the MRC (Medical Research Council) framework for developing and evaluating complex interventions refers to process evaluations as an integral part of the development of complex evidence-based interventions. Even though the need for process evaluations is recognized, the realization of such approaches is challenging because methodological instruction is sparse, and the phenomenon of interest is complex. A number of theoretical approaches indicating how to conduct process evaluations of complex interventions in health care exist, but a systematic and comprehensive overview of these is missing. Thus, the objective of the systematic scoping review described herein is to provide an overview and analysis of theoretical approaches suitable for the planning and conducting of process evaluations. METHODS: The design and conduct of this review will follow the procedures of a systematic scoping review. The search strategy will be developed following the BeHEMoTh (Behaviour of interest; Health context; Exclusions; Models or Theories) template which has been conceptualized for structured reviews of theory. The systematic search of the MEDLINE (via PubMed), CINAHL (via EBSCO) and PsycInfo (via EBSCO) electronic databases will be complemented by "hand searching" techniques. Study selection, data extraction, and data analysis will be performed by tandems of two researchers independently of each other. Divergent decisions and judgements between the two researchers will be discussed by the whole review team. DISCUSSION: The findings from this scoping review will provide an overview and comparison of theoretical approaches suitable for process evaluations of complex interventions in health care. The review results will support researchers in choosing the theoretical approach that best fits the respective focus of their process evaluation study. SYSTEMATIC REVIEW REGISTRATION: This study has been registered with PROSPERO (International Prospective Register of Systematic Reviews) under registration number CRD42020211732 .