Although the significant importance of earthworms for agriculture has been widely recognized for a long time, there is still no modern, comprehensive presentation of this animal group that is accessible to a broader audience. This is particularly regrettable, as earthworms have been the subject of numerous specialized studies from various research fields and are therefore examined in many respects more thoroughly than many other groups of invertebrates. This publication aims to fill this gap. By summarizing our current knowledge, it seeks to provide the reader with an understandable depiction of the structure, lifestyle, and development of this animal group, which lays the foundation for a true understanding of their practical significance. Furthermore, the presentation encompasses a wide-ranging framework of the interrelations.