Tiachiv is a city located on the Tisza River in Zakarpattia Oblast (region) in western Ukraine. It is the administrative center of Tiachiv Raion (district). Today, the population is 8,887.

The Tisza, Tysa or Tisa, is one of the major rivers of Central and Eastern Europe. It was once called "the most Hungarian river" because it used to flow entirely within the Kingdom of Hungary. Today, it crosses several national borders.