The morphology, anatomy, taxonomy, evolution, ecology, and behavior of major groups of fossil and extant agnathans were presented in depth, and the relevant fossil finding and research history were introduced as well. A majority of Myllokunmingiida and Galeaspida found in China, and representatives of Euconodonta and other major agnathan groups including Myxini, Petromyzontida, Arandaspida, Astraspida, Heterostraci, Anaspida, Thelodontida, Pituriaspida and Osteostraci, 47 Families, 99 genera, 107 species in total, were selected for systematic description. The data of each genus and species included diagnosis, locality, horizon, and age, accompanied by fossil photos, anatomical illustrations and ecological restorations. This book is suitable to read for both professionals of paleontology, biology, geology, and amateurs of paleontology.