Altered cell metabolism enables tumours to sustain their increased energetic and biosynthetic needs. Although tumour metabolism has long been considered a promising discipline in the development of cancer therapeutics, the majority of work has focused on changes in glucose metabolism. However, the complexity of cellular metabolism means that very rarely is an individual metabolite required for a single purpose, and thus understanding the overall metabolic requirements of tumours is vital. Over the past 30 years, increasing evidence has shown that many tumours require glutamine as well as glucose for their proliferation and survival. In this minireview, we explore the complexity of glutamine metabolism in tumour cells, discussing how the overall context of the tumour dictates the requirement for glutamine and how this can affect the design of effective therapeutic strategies.