BpForms is an ontology of molecularly-concrete DNA, RNA, and protein residues and crosslinks which can be composed into molecularly-concrete forms of DNA, RNA, proteins, and complexes. The ontology can be used with the BpForms grammar and software tools for polymers and the BcForms grammar and software tools for complexes. See https://www.bpforms.org and https://www.bcforms.org for more information.