Calderdale (/ˈkɔːldərdeɪl, ˈkɒl-/) is a metropolitan borough of West Yorkshire, England, which had a population of 211,439. It takes its name from the River Calder, and dale, a word for valley. The name Calderdale usually refers to the borough through which the upper river flows, while the actual landform is known as the Calder Valley. Several small valleys contain tributaries of the River Calder. The main towns of the borough are Brighouse, Elland, Halifax, Hebden Bridge, Sowerby Bridge and Todmorden.
Calderdale covers part of the South Pennines, and the Calder Valley is the southernmost of the Yorkshire Dales, though it is not part of the Yorkshire Dales National Park. The borough was formed in 1974 by the merger of nine local government districts.