Castleton is a village and civil parish in the High Peak district of Derbyshire, England, at the western end of the Hope Valley on the Peakshole Water, a tributary of the River Noe, between the Dark Peak to the north and the White Peak to the south. The population was 544 at the 2021 Census.

Castleton village was mentioned as Pechesers in Domesday Book in 1086 where "Arnbiorn and Hundingr held the land of William Peverel's castle in Castleton". This land and Peverel's castle were amongst the manors belonging to William Peverel that also included Bolsover and Glapwell.

St Edmund's Norman church was restored about 1837. It has late 13th-century tracery and an ashlar-faced Perpendicular tower. Its box pews are dated 1661, 1662, 1663 and 1676.

A medieval leper hospital (the Hospital of Saint Mary in the Peak) is thought to have been on the eastern boundary of Castleton, though some locals believe it to have been just south of the Speedwell Cavern footpath from the village. University of Sheffield archaeologists are investigating 'Castle of the Peak', which was reputedly founded by the wife of one of the William Peverels before 1153, and continued until about the 1543 Dissolution. They say the earliest documents referring to Spital Field are a grant and a Charter from the early 14th century. They are also investigating the 12th-century planned town at the foot of the castle hill. Castleton's medieval town defences are still evident in the village and are a Scheduled monument.

Castleton had a long history of lead mining; the Odin Mine, one of the oldest lead mines in the country, is situated 1.5 kilometres (0.9 mi) west of the village (see also Derbyshire lead mining history). Researchers studying an ice core from a Swiss glacier have found that levels of lead air pollution across Europe during the period 1170–1216 were as high as those of the Industrial Revolution, and the principal source was Peak District mines such as Castleton and Wirksworth. The mining created and enlarged local caverns, four of which are now open to the public as Peak Cavern, Blue John Cavern, Speedwell Cavern and Treak Cliff Cavern. A small amount of Blue John is mined locally and sold in local gift shops, one of which is located in the 17th-century tollhouse.

Since the 1920s the main mineral industry in the area has been cement. Hope Cement Works is closer to Hope but its quarry is closer to Castleton. A war memorial stands in the Market Place, in memory of local residents who died during both World Wars.

Castleton is situated between the gritstone plateau of the Dark Peak to the north and the gentler limestone scenery of the White Peak to the south. It lies at the western end of the Hope Valley and consequently is surrounded on three sides by hills. Most prominent is the ridge to the north. This is called Great Ridge; it runs east from Mam Tor to Back Tor and Lose Hill, via the pass (hause) of Hollins Cross, where paths from many directions converge and cross over to Edale. Alexander von Humboldt visited caves near Castleton and Buxton in June 1790 to investigate the region's geological structures.

Castleton was formerly on the A625 road from Sheffield to Chapel-en-le-Frith, on the way to Manchester. Leaving Castleton, the western road once went over Mam Tor, but after continual landslides and repairs - Mam Tor is called the "Shivering Mountain" because of its very loose shales - it was eventually abandoned. The only westbound exit from Castleton is now the unclassified road over the narrow Winnats Pass. This road is very narrow and steep and unsuitable for heavy vehicles or high volumes. Road signage has been designed to discourage through traffic by showing only local destinations. Thus most traffic enters and leaves the village on the eastern (Hope-Hathersage-Sheffield) road (A6187); traffic going west has to make a long diversion via the villages of Bradwell and Peak Forest.