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Guidance for intervention research in public health, health services and beyond, has evolved rapidly since the turn of the century. To take UK Medical Research Council (MRC) guidance for developing and evaluating complex interventions as an example, this began in 20001 with guidance for randomised controlled trials (RCTs) of complex interventions. This guidance followed a linear sequence from intervention theory towards a goal of demonstrating whether an intervention ‘worked’, and then, whether and how to implement more widely. An updated version, published in 2008,2 reflected a number of shifts in thinking. The RCT was still considered the most robust evaluation design in many cases, but the new guidance recognised that for many important interventions, RCTs are infeasible. It introduced a focus on process evaluation, recognising that while estimating effects is important, it is of limited value if we do not also know what was implemented (ie, what the intervention actually was, not just what it was ‘supposed’ to be according to the manual), or what contextual issues need to be considered where using an intervention elsewhere. The following years saw emergence of a diverse range of guidance and frameworks, including MRC guidance for natural experiments3 and process evaluations,4 and researcher-led guidance and frameworks on intervention development5–7 and adaptation of interventions to new contexts.8 In 2018, the MRC-National Institute for Health Research (NIHR) commissioned a further update to overarching guidance for the development and evaluation of complex interventions, published in 2021.9 This moved towards further pluralism in method, emphasising a role for studies focused on efficacy, effectiveness, theories of change, …