The Guhyasamāja Tantra (Sanskrit: गुह्यसमाजतंत्र, romanized: Guhyasamājatantra, lit. 'Tantra of the Secret Society/Community'; Tibetan: གསང་འདུས་རྩ་རྒྱུད, Wylie: gsang 'dus rtsa rgyud), Tōhoku Catalogue No. (Toh) 442, also known as the Tathāgataguhyaka (Secrets of the Tathagata), is one of the most important scriptures of Tantric Buddhism, written in Sanskrit. In its fullest form, it consists of seventeen chapters, though a separate "explanatory tantra" (vyākhyātantra) known as the Later Tantra (Sanskrit: गुह्यसमाज उत्तरातंत्र, romanized: Guhyasamāja Uttaratantra; Tibetan: རྒྱུད་ཕྱི་མ, Wylie: rgyud phyi ma), Toh 443, is sometimes considered to be its eighteenth chapter. Many scholars believe that the original core of the work consisted of the first twelve chapters, with chapters thirteen to seventeen being added later as explanatory material.
The Guhyasamāja-tantra is not to be confused with the Mahayana sutra titled Tathāgataguhyaka Sūtra.
