Microalgae have been largely commercialized as food and feed additives, and their potential as a source of high-added value compounds is well known. Yet, only a few species of microalgae have been genetically transformed with efficiency. A better understanding of the mechanisms that control the regulation of gene expression in eukaryotes is therefore needed. In this book a group of outstanding researchers working on different areas of microalgae biotechnology offer a global vision of the genetic manipulation of microalgae and their applications.