Same sex marriage isn't legal in Northern Ireland, but it is in the rest of the UK.
Being gay is when either two men or two women are in a relationship.
Martin went to Northern Ireland to hear from people who support and are opposed to gay marriage.
He visited a school, where some of the children told him why they feel gay people should be able to get married in Northern Ireland.
He also heard from John, who's part of an influential Christian group called the Evangelical Alliance, who don't want to see same-sex marriage introduced.