Containing nearly 200 genera and 975 species as of 2013[update], it is one of the largest families of millipedes.

[2] Paradoxosomatids occur on all continents except Antarctica, and can generally be distinguished by dorsal grooves on most body segments and a dumb-bell shaped gonopod aperture.

In males, the opening on the underside of the body where the gonopods (male reproductive appendages) attach has a central constriction, forming the shape of an hourglass or dumb-bell.

Males of most species also possess one or two projections on the sternite of the fifth body segment.

Widely introduced species in the tropics include Asiomorpha coarctata (native to Southeast Asia) and Chondromorpha xanthotricha, native to Sri Lanka or southern India.