The Roman Catholic church has constituent churches in which married priesthood is the typical path. The Latin Catholic church, which, with over a billion members, is the largest constituent of the Roman Catholic church, only ordains single men to the priesthood. In all apostolic churches (I believe), an ordained priest cannot marry after ordination without some kind of special dispensation. Also, both Catholic and Orthodox only ordain celibate men to the episcopacy.

However, there is no rule that this is the case. Any man can be ordained a priest or bishop, married or not.