The Kasimovian is a geochronologic age or chronostratigraphic stage in the ICS geologic timescale.
It is the third stage in the Pennsylvanian (late Carboniferous), lasting from 307 to 303.7 Ma.
The Kasimovian saw an extinction event which occurred around 305 mya, referred to as the Carboniferous Rainforest Collapse.
The stage was split from the Moscovian in 1926 by Boris Dan'shin (1891-1941), who gave it the name Teguliferina horizon.
The name was posthumously changed to Kasimov horizon by Dan'shin in 1947.