Euboea or Evia is the second-largest Greek islandin area and population, after Crete. The narrow Euripus Strait separates it from Boeotia in mainland Greece. In general outline it is a long and narrow island; it is about 180 kilometres (110 mi) long, and varies in breadth from 50 kilometres (31 mi) to 6 kilometres. Its geographic orientation is from northwest to southeast, and it is traversed throughout its length by a mountain range, which forms part of the chain that bounds Thessaly on the east, and is continued south of Euboea in the lofty islands of Andros, Tinos and Mykonos.

It forms most of the regional unit of Euboea, which also includes Skyros and a small area of the Greek mainland.