A commitment ceremony is held to mark the union between two people who are not legally allowed to marry. Gay men and lesbians routinely participate in commitment ceremonies.
Although commitment ceremonies mean different things to different people, they are often very similar to traditional wedding ceremonies. Participants can choose to wear wedding attire like a wedding dress, and these ceremonies may even take place in a church setting. The only real difference is that it is not a legally binding ceremony.
Some couples prefer to have their commitment ceremony performed by a religious figurehead, such as a priest or rabbi. Although unions, such as those between two gay men, is typically frowned upon by many churches, it may be easier to find a priest or rabbi to conduct the ceremony if that person is familiar with those wishing to engage in the ceremony. Often, alternative religions are more accepting of those who can't marry in a traditional setting.
As with any wedding ceremony, there can be music, vows, the exchanging of rings and a reception at a commitment ceremony. It is up to the participants how simple or extravagant the ceremony will be. Many people refer to a commitment ceremony as a 'wedding" or a "ceremony of union."