中古希腊语，又被称作拜占庭希腊语，是指从公元7世纪到1453年君士坦丁堡的陷落为止的这一时期的希腊语。从7世纪起希腊语就作为拜占庭帝国唯一的管理和行政语言。所以对中古希腊语及其文学的研究也是拜占庭研究的一部分。

中古希腊语的开端可以追溯到4世纪或者330年罗马帝国首都迁移到君士坦丁堡或者395年罗马帝国的分裂。但是这样的划分并不能反映语言发展的真实情况。只有当东罗马帝国的文化在7世纪发生重大改变的时候才能算作这一语音的开端。中古希腊语是连接古典希腊语和现代希腊语的重要纽带，一方面在文学上受到古典希腊语的强烈影响，另一方面很多现代希腊语的语言特征开始在口语中出现。

Medieval Greek, also known as Byzantine Greek, is the stage of the Greek language between the end of Classical antiquity in the 5th-6th centuries and the end of the Middle Ages, conventionally dated to the Ottoman conquest of Constantinople in 1453. From the 7th century onwards, Greek was the only language of administration and government in the Byzantine Empire. This stage of language is thus described as Byzantine Greek. The study of the Medieval Greek language and literature is a branch of Byzantine Studies, or Byzantinology, the study of the history and culture of the Byzantine Empire.