This book represents a unique combination of recently-emerged information on eukaryotic microbes, evolution and genomics. Eukaryotes, cells with nuclei, evolved as microbes and have existed on Earth for approximately 2 billion years. Although currently relatively understudied, eukaryotic microorganisms are of critical importance to ecosystems (through their involvement in global biogeochemical cycles), human health (they include some of the deadliest pathogens), and our desire to understand global biodiversity. Recent advances, particularly in DNA sequencing technologies, are making eukaryotic microbes more accessible through genome analyses. Insights from these studies are challenging previously held theories of genome evolution, based on studies of a limited number of plants, animals and fungi.