Microalgae biotechnology is an emerging field of research and a viable option for developing environmentally friendly technologies. The immense potential of the biotechnological applications based on different microalgae has fostered a wave of research on their potential as a sustainable resource for products and solutions for human and animal nutrition, aquaculture, agriculture, biofuels, and emergent areas such as cosmetics and pharmaceuticals. “In this context”, the market is still developing for most of these applications, and intensive research is necessary to unlock microalgae biotechnology’s full potential. In light of it all, we present a retrospective on microalgae biotechnology in this chapter. Microalgae-based products and solutions that have overcome the valley of death and those that have not yet crossed it are addressed. An overview of microalgae biotechnology’s various promises and limitations is also presented.