It is my understanding that the groom’s parents pay for the rehearsal dinner, my question is this, “exactly who does this include?”, bridesmaids and spouses, out of town guests as well, the parents of the ringbearer, etc. or are they responsible for picking up the tab for just the wedding party members? this can be quite expensive if everyone is included.

Donna, Wedding Queen, President; Top Wedding Sites

Typically, the grooms parent’s do host the rehearsal dinner, though it is not mandatory. As the hosts they would pay for anyone attending. You should invite everyone included in the wedding ceremony (ushers, bridesmaids, bestman, maid of honor, flowergirl, ring bearer, officiate, etc.) Spouses or dates of all adult attendants should be invited. Parents (divorced parents new spouses or partners), grandparents and siblings of the bride and groom should be invited. If children are involved in the wedding, the children and their parents should be invited. If there are out of town guests staying over it could be considerate to invite these people as well, however not required, especially if there are many out of town guests.

This could get expensive depending on the restaurant they choose, IF they even choose to hold the dinner at a restaurant. They could have the dinner at their home (if they have the room) and have it catered or a barbeque in the backyard. The main purpose is to offer the bridal party and those who need to rehearse, some refreshments after the rehearsal to thank them for supporting you during the planning.