The first modern Hindu reform movement, the Brāhmo Samāj (initially known as the ‘Brāhmo Sabhā’) was founded in Calcutta in 1828 by the Bengali intellectual Rāmmohun Roy. Reorganized by Debendranāth Tagore in 1843, it split in 1866 into Tagore's Ādi Brāhmo Samāj (‘Original Brahman Association’) and Keshab Chandra Sen's ‘Brāhmo Samāj of India’. In 1878 the latter movement abandoned Keshab and reformed itself as the Sādhāraṇ (‘General’) Brāhmo Samāj.
In response to Christian missionary work and Western scientific rationalism, the general aims of the movement were to fashion a reformed and universalized ‘real Hinduism’, shorn of what Roy regarded as its superstitious and idolatrous practices (pūjā and temple ritual), and returned to its pure, monotheistic origins, as represented in his reading of the Upaniṣads and other Vedānta aligned texts. Alongside this theological agenda, the Brāhmo Samāj aimed to reform those social practices that Roy saw as concomitant with ‘idol worship’ and polytheism. Widow burning (satī), polygyny, child marriage, infanticide, caste discrimination, and the lack of female education were all subject to criticism and active campaigning. After Roy's death, the theological stance of the Society began to shift under the leadership of Tagore. In 1843 he instituted a ‘Brāhmo Covenant’ requiring members to worship one God. However, it became increasingly clear, in the light of criticism from Christians, rationalists within the movement, and Hindu traditionalists, that only a very selective reading of the Vedas (such as that employed by Roy) could provide textual support for such a deity, and Tagore reluctantly jettisoned reliance on the authority of Sanskrit texts. This process was accelerated under the influence of Keshab Chandra Sen, who joined the Brāhmos in 1858. The group that gathered itself around him was much more radical in its rejection of traditional Hindu practices and attitudes than Tagore's followers, and took an aggressively missionary stance, drawing on Western models while rejecting the Christianity of the missionaries. The tension between the two groups within the Samāj resulted in the split of 1866. Sen became ever more idiosyncratic in his religious practice, and increasingly indifferent to social reform. This led to his abandonment by many of his followers, who formed the Sādhāraṇ Brāhmo Samāj in 1878. Sen himself gathered the remnant into the ‘Church of the New Dispensation’ in 1881. In the meantime, Tagore's Ādi (‘original’) Brāhmo Samāj had dwindled into little more than an association of family and friends. Despite its disintegration as a Society, the Brāhmo Samāj's influence persisted. The questions it raised about the ‘true’ nature of Hinduism were taken up by other organizations, such as the Ārya Samāj, and thereby helped to generate the movement for Indian independence. See also Neo-Hinduism.