Caenogastropoda is a taxonomic subclass of molluscs in the class Gastropoda. It is a large diverse group which are mostly sea snails and other marine gastropod mollusks, but also includes some freshwater snails and some land snails. The subclass is the most diverse and ecologically successful of the gastropods.

Caenogastropoda contains many families of shelled marine molluscs – including the periwinkles, cowries, wentletraps, moon snails, murexes, cone snails and turrids – and constitutes about 60% of all living gastropods.

The Caenogastropoda exhibit torsion, and thus are included in what was previously called the Streptoneura (meaning twisted nerves), also known as Prosobranchia (meaning gills forward). Specifically, they are characterized by having only a single auricle in the heart and a single pair of gill leaflets, and are equivalent to the Monotocardia or Pectinibranchia of older authors.

The taxon Caenogastropoda was first established by Leslie Reginald Cox in 1960 as a superorder but now sometimes it is retained as a clade. Based on optimal phylogenetic analysis, it is deemed monophyletic. This Caenogastropoda combines the older taxa Mesogastropoda and Stenoglossa from the classification by Johannes Thiele and is equivalent to the revised Monotocardia as defined by Mörch in 1865.

Caenogastropoda can be divided into two major groups, based on the anatomy of the radula:

Ponder & Lindberg, 1997 and others since (e.g. Vega et al., 2006; Harzhauser, 2004; and Pina, 2002.) show Caenogastropoda as a superorder, following the sense of Cox, 1960. More recently Bouchet & Rocroi, 2005 revised Caenogastropoda as a clade.

The following classification was laid out in the taxonomy of Bouchet & Rocroi (2005):

Colgan et al. (2006) provided further insight into the phylogeny of Caenogastropoda.