The name Old Ruthenian language has been applied to different things.

• Old East Slavic language was the language of Kievan Rus', spoken from the 9th to 14th centuries. It was the ancestor of the East Slavic languages Belarusian, Russian, Rusyn, and Ukrainian.
• Ruthenian language was its descendent which was spoken in the historic Grand Duchy of Lithuania from the 15th to 18th centuries. It was the ancestor of modern Belarusian, Rusyn, and Ukrainian languages.