Managerial carbon accounting (MCA) is a set of accounting-based technical tools and methods that enable managers to strengthen decarbonisationDecarbonization decision-making. It is designed to help internal staff within an entity, whereas financial carbon accounting (FCA) is primarily for the information nseeds of external users. This chapter develops a theoretical underpinning for the concept and practice of the emerging system and highlights the differences between MCA and FCA in terms of its objectives, functions, and methodology. Further elaborations focus on six structural components of MCA: Cost of carbon mitigation; capital expenditure on green projects; carbon budgets; carbon performance evaluation; internal carbon reporting. Note that the operation of all the components of MCA is based on quantified GHG emissions. MCA can be tailored for firms in specific circumstances and assist managers to enhance capacity to achieve GHG reduction and energy efficiency, and at the same time to minimise costs of decarbonisationDecarbonization.