This chapter examines the psychological factors that influence sustainable consumption behaviour, focusing on the intersection of commerce and individual consumer choices. As sustainability initiatives gain prominence, various industries have faced public scrutiny due to the significant environmental damage they cause throughout their life cycles. Despite increased awareness of these negative externalities, consumers continue to purchase goods to satisfy their needs and desires. Analysing the psychological processes that motivate sustainable purchasing practices is essential to tackle these challenges. Discussions surrounding the theory of planned behaviour have highlighted several psychological frameworks that initiate responsible consumer choices, ranging from individual moral beliefs to the effects of social influences. Based on empirical studies, this chapter examines how attitudes, subjective norms, and perceived behavioural control influence sustainable consumption intentions and behaviours in various contexts, using statistical tools to test these relationships. Finally, the implications are discussed, focusing on strategies to promote sustainable consumption behaviour. Marketers and researchers can help consumers develop these psychological insights with some recommendations for firms that seek to offer sustainable products and provide structural support for their initiatives.