Nejdek (Czech pronunciation: [ˈnɛjdɛk]; German: Neudek) is a town in Karlovy Vary District in the Karlovy Vary Region of the Czech Republic. It has about 7,700 inhabitants.

Nejdek consists of ten municipal parts (in brackets population according to the 2021 census):

The name originated from German neue Decke, i.e. 'new cover'. It was derived from the newly covered roof of the castle tower.

Nejdek is located about 13 kilometres (8 mi) northwest of Karlovy Vary. It lies in the west of the Ore Mountains. The highest point is the mountain Tisovský vrch at 977 m (3,205 ft) above sea level. The Rolava river flows through the town.

Nejdek was founded around 1250 as a tin mining settlement. The first written mention of Nejdek is from 1340. During the golden era of tin mining in the 14th–16th century, the town experienced its greatest expansion. From 1446 to 1602, it was owned by the Schlick family. During their rule, iron ore also began to be mined, and smelters and hammer mills were established in the area.

In 1602–1633, the Nejdek estate was owned by the Collon family, and violent re-Catholicization took place. During this period, many inhabitants left and there was a decline in mining.

In the 19th century, the town was industrialized. Ironworks and spinning mill were established. In 1899, the Karlovy Vary–Johanngeorgenstadt railway was put into operation.

Nejdek is located on the Karlovy Vary–Johanngeorgenstadt railway line. The municipal territory is served by six train stations and stops.