Great Wallachia (Greek: Megale Vlachia; Romanian: Vlahia Mare), also Thessaly Wallachia, was a medieval state (12th and 13th century) of the Aromanian (Vlach) shepherds, which included the Thessaly region of Greece, the southern and central ranges of Pindus and extending over part of Macedonia.

Anna Comnena in the second half of the 11th century was the first author to write about the Vlach settlements of the mountains of Thessaly. Benjamin of Tudela, the next century, wrote the earliest account of the independent state of "Great Wallachia" in the mountains. He wrote that "No man can go up and battle against them and no king can rule over them".

After the Latin conquest of Constantinople in 1204, Great Walachia was included in the enlarged despotate of Epirus, but it soon reappears as an independent principality under its old name.