This chapter provides an overview of the past, present, and future of microalgae, tracing their evolution from essential contributors to the Earth’s ecosystem to their modern role as key players in biotechnology and sustainability. Here, we describe the early scientific interest in microalgae as potential sources of food and biofuels, highlighting significant advances in cultivation and industrial applications over the years. The chapter also discusses current advances in microalgae-based systems for the production of biofuels, food, pharmaceuticals, and other bioproducts, and environmental bioremediation. Future challenges and the promising potential of large-scale production of microalgae for the creation of a circular bioeconomy are also discussed.