This is a vade mecum of terms for describing all aspects of sponge morphology, such as habit, surface structure, consistency, and anatomy. Definitions of microscopic features include aquiferous system, cytology, reproductive structures, skeletal architecture, and calcareous and siliceous spicules. Terms were selected and reviewed by an international group of 10 experts in sponge systematics, during several workshops. Each entry is accompanied by a precise diagnosis and an illustration. Terms listed as “rejected” are those judged unsuitable, redundant, or preoccupied. The thesaurus will aid descriptions in future systematic papers, computerized data banks, and identification keys. The literature cited presents a historical perspective on similar attempts to create a precise terminology of sponge morphology and helps to further clarify the selected terms.