The advertising agency supplies media to clients by purchasing media from magazine publishers, broadcast stations, and other media forms; these could include outdoor (billboards), transit, etc. The media department of the agency plans the media buy, sets the goals and objectives, and then executes the "buy" on behalf of the client.

For this service, the advertising agency usually charges a commission of 15%. On occasion, a fee will be negotiated.

When a barter company supplies media directly to a client, the media department of the ad agency should still be involved in the planning phase of the media (even though it will not be calling all the stations and placing the orders). Since the agency does not have to get involved in negotiating with the stations and with magazines (the most costly part of the agency's involvement), it will usually accept a smaller percentage of the entire buy for its more limited involvement.