Ajka (Hungarian pronunciation: [ˈɒjkɒ]) is a city in Hungary with about 35,000 inhabitants.

The village Ajka was named after the Ajka clan, which, in turn, got its name after its ancestor, a knight named Heiko, who was a member of the retinue of Gisela, Princess of Bavaria, wife of King St. Stephen in the early 11th century.

Real prosperity came only in the second half of the 19th century, when coal resources were found nearby.

In the following decades, four additional villages (Csékút, Bakonygyepes, Padragkút, and Ajkarendek) were annexed to the town.

A flood of bauxite tailings occurred in 2010, releasing 600,000 to 700,000 m3 (21,188,800 to 24,720,267 cu ft) of red caustic toxic industrial sludge, which affected some 40 km2 (15 sq mi); 10 people were killed and 150 were injured.