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.

Halifax is the commercial, cultural and administrative centre of the borough. Calderdale is served by Calderdale Council, which is headquartered in Halifax, with some functions based in Todmorden.

The Roman settlement of Cambodunum is traditionally associated with the Calderdale area, though its precise location remains a matter of debate. Archaeological excavations have identified a Roman fort and associated civilian settlement (vicus) at Slack, now within the neighbouring borough of Kirklees, which many historians equate with Cambodunum mentioned in Roman itineraries such as the Antonine Itinerary. However, because Slack lies outside the modern boundaries of Calderdale and because the exact correspondence between archaeological sites and Roman place-names is not always certain, the identification of the fort at Slack as Cambodunum is not universally accepted. As a result, while Cambodunum is often described as being located in or near Calderdale, its precise siting remains unresolved in academic literature.

The metropolitan district of Calderdale was created on 1 April 1974 under the Local Government Act 1972. It covered the area of eight former districts and part of a ninth, which were all abolished at the same time:

The area of the new district broadly corresponded to the ancient extent of the parish of Halifax, though not exactly.

In 2022, Yorkshire Water built an emergency water pipeline from Calderdale to Ponden Reservoir in Haworth as Yorkshire experienced its driest period on record.

The borough is divided into 17 wards, each of which is represented on Calderdale Metropolitan Borough Council by three councillors. Councillors are normally elected using the first-past-the-post system for four-year terms, with elections staggered so that only one councillor per ward is elected in any given year. Exceptions to this arrangement include by-elections and elections held following ward boundary changes.