The Cyrillic script ( /sɨˈrɪlɪk/) or azbuka is an alphabetic writing system developed in the First Bulgarian Empire during the 10th century AD at the Preslav Literary School. It is the basis of alphabets used in various languages, past and present, in Eastern Europe and Asia, especially those of Slavic origin, and non-Slavic languages influenced by Russian. As of 2011 around 252 million people in Europe and Asia use it as official alphabet for their national languages. About half of them are in Russia.

Cyrillic is derived from the Greek uncial script, augmented by ligatures and consonants from the older Glagolitic alphabet and Old Bulgarian for sounds not found in Ancient Greek. It is named in honor of the two Eastern Roman Empire brothers, Saints Cyril and Methodius, who created the Glagolitic alphabet earlier on. Modern scholars believe that Cyrillic was developed and formalized by early disciples of Cyril and Methodius (such as Clement of Ohrid).

With the accession of Bulgaria to the European Union on 1 January 2007, Cyrillic became the third official script of the European Union, following the Latin and Greek scripts.