Theories provide a way of understanding and predicting the effects of patient safety practices (PSPs), interventions intended to prevent or mitigate harm caused by healthcare or risks of such harm. Yet most published evaluations make little or no explicit reference to theory, thereby hindering efforts to generalise findings from one context to another. Theories from a wide range of disciplines are potentially relevant to research on PSPs. Theory can be used in research to explain clinical and organisational behaviour, to guide the development and selection of PSPs, and in evaluating their implementation and mechanisms of action. One key recommendation from an expert consensus process is that researchers should describe the theoretical basis for chosen intervention components or provide an explicit logic model for 'why this PSP should work.' Future theory-driven evaluations would enhance generalisability and help build a cumulative understanding of the nature of change.