This book is divided into three thematic areas. The first covers a revision of the taxonomy of algae, based on the algae portal, as well as the general aspects of biology and the methodologies used in this branch of marine biology. The second subject area focuses on the use of algae in environmental assessment, with an intensive implementation in Western economies and some emerging economies. The third topic is the potential use of algae in various industries including food, pharmaceuticals, cosmetics, agricultural fertilizers, and the emerging biofuels industries.