Background: More older people are living in the community with multiple diagnoses and medications. Managing multiple medications produces issues of unrivalled complexity for those involved. Despite increasing literature on the subject, gaps remain in understanding how, why and for whom complex medication management works, and therefore how best to improve practice and outcomes. MEMORABLE, MEdication Management in Older people: Realist Approaches Based on Literature and Evaluation, aimed to address these gaps. Methods: MEMORABLE used realism to understand causal paths within medication management. Informed by RAMESES (Realist And Meta-narrative Evidence Synthesis: and Evolving Standards) guidelines, MEMORABLE involved three overlapping work packages: 1) Realist Review of the literature (24 articles on medication management exploring causality); 2) Realist Evaluation (50 realist-informed interviews with older people, family carers and health and care practitioners, explaining their experiences); and 3) data synthesis and theorising from 1) and 2). Results: Medication management was viewed from the perspective of ‘implementation’ and structured into five stages: identifying a problem (Stage 1), getting a diagnosis and/or medications (Stage 2), starting, changing or stopping medications (Stage 3), continuing to take medications (Stage 4), and reviewing/reconciling medications (Stage 5). Three individual stages (1, 3 and 4) are conducted by the older person sometimes with family carer support when they balance routines, coping and risk. Stages 2 and 5 are interpersonal where the older person works with a practitioner-prescriber-reviewer, perhaps with carer involvement. Applying Normalisation Process Theory, four steps were identified within each stage: 1) sense making: information, clarification; 2) action: shared-decision-making; 3) reflection/monitoring; and 4) enduring relationships, based on collaboration and mutual trust. In a detailed analysis of Stage 5: Reviewing/reconciling medications, adopting the lens of ‘burden’, MEMORABLE identified five burdens amenable to mitigation: ambiguity, concealment, unfamiliarity, fragmentation and exclusion. Two initial improvement propositions were identified for further research: a risk screening tool and individualised information. Conclusions: Older people and family carers often find medication management challenging and burdensome particularly for complex regimens. Practitioners need to be aware of this potential challenge, and work with older people and their carers to minimise the burden associated with medication management.