The Kitáb-i-Aqdas ("The Most Holy Book") is the central book of laws revealed by Bahá'u'lláh, the founder of the Bahá'í Faith, written in Arabic around 1873 during His exile in 'Akká (in present-day Israel). It serves as the foundation of Bahá'í law and governance, combining legal ordinances, ethical teachings, and spiritual exhortations. The book addresses both individual responsibilities and broader social principles. Among the key personal laws are obligatory daily prayer, a nineteen-day fast, monogamy, and rules concerning inheritance, marriage, and burial. Yet Bahá'u'lláh's approach to law is not rigid or punitive; many laws are given in a tone of loving guidance, emphasizing the spiritual benefits of obedience rather than enforcement through fear. Bahá'u'lláh also sets a tone of mercy and flexibility, leaving interpretive authority to future institutions like the Universal House of Justice, which He established as part of the Faith's administrative framework.

At a societal level, the Kitáb-i-Aqdas lays the groundwork for a future global civilization unified by spiritual principles. It calls for the elevation of the station of women, the abolition of prejudice, the pursuit of justice, and the need for universal education. The book proclaims the coming of the "Most Great Peace" and anticipates a world governed by spiritual unity rather than sectarian division or national rivalry. It discourages religious fanaticism, asceticism, and clergy-dominated religious authority, instead promoting direct personal engagement with sacred texts. The Aqdas also introduces fundamental Bahá'í concepts such as the Covenant, through which authority is transferred to 'Abdu'l-Bahá and the institutions of the Faith. The text blends legal clarity with mystic vision, balancing divine command with human dignity. As such, it is not merely a lawbook but a spiritual charter for a global, just, and unified society rooted in faith and reason.