Using a multicharacter approach and numerical cladistic computer programs a phylogenetic analysis is made of a newly defined order Halichondrida (which includes all Halichondrida and parts of the Axinellida sensu Levi, 1973), with emphasis on the newly defined family Halichondriidae (which includes the families Halichondriidae and Hymeniacidonidae sensu Levi, 1973, and some genera formerly assigned to the Axinellidae and Desmoxyidae). The newly defined order consists of the "old" families Axinellidae/Bubaridae and Desmoxyidae, a "new" family Dictyonellidae, and the new concept of the family Halichondriidae. Next to classical morphological characters also biochemical data (secondary metabolites) were used. This resulted in the recognition of several discrete generic groups, viz. Axinyssa + Collocalypta, Myrmekioderma + Didiscus, Spongosorites, Topsentia + Epipolasis + Petromica, Ciocalypta + Amorphinopsis, and Hymeniacidon + Halichondria. A revision comprising definitions of and remarks on all genera, including all junior synonyms, of the newly defined Halichondriidae concludes the paper.