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

[citation needed] The large nidoviruses encode both a 2'-O-methyltransferase and a 3'–5' exoribonuclease (ExoN)—the latter being very unusual for an RNA virus.

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