Meeting the enormous challenge of decarbonising world energy systems will require a rapid expansion of investment in clean technologies on a global scale. Mobilising these resources will be a daunting task, and it is important to undertake the transition at the lowest cost possible. This paper seeks to provide some guidance on climate change policy‐making within real‐world constraints, focusing on the justification of policies to supplement a carbon price (arising from an emissions trading system or carbon tax), interactions between carbon pricing and supplementary policies, and management of these interactions to enable a least‐cost policy response.