Käsmu (German Kasperwiek, Hasterwieck) is a village in northern Estonia in the Lääne-Virumaa county, Haljala parish. Before the administrative-territorial reform of 2017, it was part of Vihula parish.

Käsmu was first mentioned in 1453 as a coast belonging to the Aaspere manor (strand tho Kesemo).

The first information about the village dates back to the beginning of the 16th century (1524 - Kazmekul), subsequent data - to the beginning of the 18th century. In 1726, there were 9 peasant families and 6 families of free people in the village; in 1871 there were 19 households. In 1782, 153 people lived in the village, in 1858 - 195.

Käsmu has been known since ancient times as a port village and a shipbuilding site. The first ship was built in Käsmu in 1697.

In the middle of the 19th century, the owners of Aaspere Manor built the first summer cottages in Käsmu.

In 1884-1931 there was the Käsmu Naval School, in which 1,664 cadets studied over the years, of which more than 500 became captains and navigators, 64 - sea captains. The wooden one-storey school building with an attic is currently restored according to old photographs and entered in the State Register of Cultural Monuments of Estonia.

In 1891 a wooden lighthouse was built in Käsmu and the ship "Salme" (Est. Salme), which crossed the ocean. The lighthouse is included in the Estonian State Register of Cultural Monuments.

The Lungins' family, Anastasia Tsvetaeva, Moscow conceptualists and many others rested in Käsmu.

The Käsmu Maritime Museum (est. Käsmu Meremuuseum) is located in Käsmu.

Since 2008, the Viru Folk music festival has been held in Käsmu.

Legend of the founding of Käsmu
The legendary founding father of the village is Captain Kaspar. He drove his ship across the sea along the coast. Near the territory of present-day Käsmu, the ship was caught in a strong storm and wrecked. Of the whole team, only Kaspar made it to the shore, he offered up a prayer for salvation and vowed to build a chapel on this very spot.