This chapter explores the intricate relationship between coffee consumption and type 2 diabetes mellitus (T2DM). With the rising prevalence of diabetes mellitus globally, understanding the potential impact of lifestyle factors such as coffee drinking is crucial. This chapter delves into the biochemical mechanisms by which coffee components, including caffeine, polyphenols and antioxidants, may influence insulin sensitivity and glucose metabolism. It also examines epidemiological data suggesting a possible inverse relationship between coffee intake and the risk of developing T2DM. Furthermore, this chapter discusses the effects of coffee consumption on gestational diabetes mellitus (GDM) and its implications for maternal and foetal health. Through a comprehensive review of clinical studies, this chapter aims to provide insights into how coffee consumption may affect diabetes management and prevention strategies.