This study explores how and why organisations invest in workplace mental health and wellbeing, combining a systematic review with an in-depth case study. It shows that decisions are rarely driven by evidence alone. Instead, investment is shaped by a mix of legal responsibility, business priorities, reputation, and beliefs about productivity. The research highlights a staged but non-linear process, including building leadership buy-in, allocating resources, implementing initiatives, and ongoing evaluation. Importantly, decisions are often influenced by internal data, culture, and intuition rather than formal evidence, reinforcing that workplace wellbeing is shaped as much by organisational context as by research.