Microalgal biotechnology has emerged due to the health-promoting properties of microalgae related to their bioactive compounds and the great diversity of products that can be developed from algal biomass. Microalgal biomasses have been produced industrially for applications in different fields such as food, pharmaceutical, nutraceutical, cosmetic, and animal feed industries. They can be cultivated either in open systems or in closed systems (photobioreactors). Another important area is the use of microalgal biomass for energy production. It has become obvious that petroleum-derived fuels are unsustainable, due to depleting world reserves and greenhouse gas emissions. Microalgae can provide several different types of renewable biofuels. These include methane produced by anaerobic digestion of the algal biomass, biodiesel derived from trans-esterification of microalgal lipids, bioethanol produced from carbohydrate fermentations, and photobiologically produced biohydrogen. The idea of using microalgae as a source of fuel is not new. However, it is now being taken seriously because of increases in petroleum prices and, more significantly, the increasing concern about global warming as associated with burning fossil fuels. This review offers an update on information about microalgae, specifically emphasizing their biotechnological importance.