This episode considers how 'systems thinking' tools, methods and approaches have been used in health policy and systems research, and how systems thinking is both 'art' and 'science'. We speak to two experts with experience applying systems thinking in a variety of health contexts and ask 'what represents 'scientific rigour' in health systems science?'.  Guests: Karl Blanchet, Director of the Geneva Centre of Humanitarian Studies, University of Geneva, and co-editor of Systems thinking for health systems strengthening: a methodological handbookKara Durski, epidemiologist and systems thinker affiliated with the World Health Organization and the School of Public Health at the University of Minnesota