立陶宛大公国（拉丁语：Magnus Ducatus Lituania，立陶宛语：Lietuvos Didžioji Kunigaikštystė）是一个存在于12世纪（或13世纪）至1569年间的欧洲君主制国家，随后该国成为了波兰立陶宛联邦的组成部分，直到1793年五三宪法被颁布，其独立地位被废除，以使联邦统一。该国由立陶宛人所创建，而立陶宛人是起源于奥克什泰蒂亚的波罗的语族部落之一，信奉多神教。大公国后来向基辅罗斯故土与其他斯拉夫土地扩张，其国土涵盖现今的白俄罗斯、拉脱维亚、立陶宛、乌克兰，以及爱沙尼亚、摩尔多瓦、波兰和俄罗斯的西部地区。15世纪，该国领土达到顶端，是当时欧洲的最大国家。它是多民族多信仰的国家，在语言、宗教和文化传统上体现出很大的多样性。

The Grand Duchy of Lithuania was a European state from the 13th century until 1795. The state was founded by the Lithuanians, one of the polytheistic Baltic tribes from Aukštaitija.

The Grand Duchy later expanded to include large portions of the former Kievan Rus' and other Slavic lands, covering the territory of present-day Belarus, Latvia, and Lithuania, and parts of Estonia, Poland, Russia, and Ukraine. At its greatest extent in the 15th century, it was the largest state in Europe. It was a multi-ethnic and multi-confessional state with great diversity in languages, religion, and cultural heritage.