Host organisms include mammals, birds, reptiles, amphibians, fish, arthropods, molluscs, and helminths.

[2] Member viruses have a viral envelope and a positive-sense, single-stranded RNA genome which is capped and polyadenylated.

[citation needed] Nidoviruses can be distinguished from other RNA viruses by a constellation of seven conserved domains—5'-TM2-3CLpro-TM3-RdRp-Zm-HEL1-NendoU-3'—with the first three being encoded in ORF1a and the remaining four in ORF1b.

[citation needed] Most, but not all, nidovirus subgenomic RNAs contain a 5′ leader sequence derived from the 5′ end of the genomic RNA.

Group member planarian secretory cell nidovirus (PSCNV) has the largest known nonsegmented RNA genome of 41.1kb.