Energy consumption in machining contributes a significant part of manufacturing cost and produces a great environmental impact. This paper provides a critical assessment on energy consumption in a machining system. Energy consumption is classified at the process, machine, and system levels. Machine tool power demand at different machine states by different components is also discussed. Then predictive methods of energy consumption at different levels are summarized. Finally, energy consumption reduction strategies are discussed to achieve sustainable manufacturing. •Energy consumption is classified at the process, machine, and system levels.•The concept of net cutting energy is established.•Empirical and analytical models of energy consumption are critically analyzed.•The strategies for reducing energy consumption are recommended.