Heaven's Gate was an American new religious movement known primarily for the mass suicides committed by its members in 1997. Commonly designated a cult, it was founded in 1974 and led by Bonnie Nettles (1927–1985) and Marshall Applewhite (1931–1997), known within the movement as Ti and Do, respectively. Nettles and Applewhite first met in 1972 and went on a journey of spiritual discovery, identifying themselves as the two witnesses of Revelation, attracting a following of several hundred people in the mid-1970s. In 1976, a core group of a few dozen members stopped recruiting and instituted a monastic lifestyle.

A new religious movement (NRM), also known as alternative spirituality or a new religion, is a religious or spiritual group that has modern origins and is peripheral to its society's dominant religious culture. NRMs can be novel in origin or they can be part of a wider religion, in which case they are distinct from pre-existing denominations. Some NRMs deal with the challenges that the modernizing world poses to them by embracing individualism, while other NRMs deal with them by embracing tightly knit collective means. Scholars have estimated that NRMs number in the tens of thousands worldwide. Most NRMs only have a few members, some of them have thousands of members, and a few of them have more than a million members.