The Special Issue Humusica 1 corresponds to a field guide for the classification of terrestrial humus systems and forms. The present first article of the issue defines vocabulary, objects and concepts necessary for: (a) field investigation, (b) understanding the process of classification, (c) assigning ecological significance to the defined morpho-functional units, (d) discussing and exchanging scientific data about humus systems. The article starts with general considerations, as the necessity humans have to classify natural objects for sharing ideas and information on them. Then the article focuses on soil as functional element of every ecosystem. Historical and recently published international definitions of soil are reported and compared to the more biological definition of the authors of the paper. Once the concept “soil” is clarified, the soil profile is shared in three new sub-units, for further specialised investigations. The superficial and organic-rich sub-unit is labelled Humipedon. In the rest of the article, authors explain the different constituents of a general humipedon, introducing even novice soil scientists to field practice and topsoil observation. A general overview of the variety of humipedons that one may expect to find all over planet Earth, classified in humus systems and forms, concludes the article.