ISLAM

Muslims had earlier interaction with Hindus than other world religions.  Conflicts with Islamic settlements motivated Hindus to begin recording Hindu doctrine.  These conflicts also inspired Hindu regional kingdoms to band together to preserve Hindu values.  Despite the conflict, there are similarities between the two religions, such as Islamic Sufism and Hindu bhakti: both promote devotion to a god.

Buddhism

Both Buddhism and Hinduism originate in India.  The two religions share the practice of yoga and the belief in rebirth.  In addition, Hindus sometimes recognize Buddha as an incarnation of Vishnu.

Christianity

While Christians look down on some Hindu practices (child marriage, image worship), Hindus disagree with the exclusivity of Christianity, but many accept Christian concepts such as morality.  India also fell under Christian influence as a part of the British Empire.