Theories and concepts from other fields than implementation science can contribute to improved understanding of the challenges of implementing evidence-based interventions, programmes, services and various practices. Implementation science could benefit from a broader dialogue with a variety of theoretical and conceptual orientations. This chapter provides a select overview of potentially relevant theories and concepts that relate to the individual level (e.g. social-cognitive theories and dual process theories), social group level (e.g. leadership and culture) and organization level (e.g. organizational learning and complexity theory). Key features and principles of theories and concepts from miscellaneous fields are described and their relevance for potential use in implementation science is discussed. © 2024 selection and editorial matter, Per Nilsen; individual chapters, the contributors.