<p>Climate-friendly intentions often fail to translate into action. In this Review, we synthesize evidence as to what shapes the intention–behaviour relationship and propose a tripartite framework of explanatory mechanisms—intrapersonal, social and structural. Intrapersonal mechanisms include cognitive biases, emotion-based drivers and behavioural habits; social mechanisms encompass norms, identity and visibility; and structural mechanisms involve affordability, convenience and systems-based trust. For each category, we review evidence-based interventions that increase follow-through, offering actionable insights for policymakers and practitioners. The challenge is to draw from this intervention toolbox appropriately and to understand boundary conditions. By diagnosing diverse psychological and contextual barriers to climate action, this paper provides a road map for closing the intention–behaviour gap, thus helping transform public will into meaningful climate action.</p>