SST and Band guys....Concert Touring question.

Currington had a Opening Act last night who was VERY good. A very young....23 years old...new guy to the Country scene. Max McNown is his name. My Wife asked the question......... WHO decides on an Opening Act. I know it's a way for New Performers to get noticed but is it the choice of the Main Performer?? Do Record Labels make it happen??? Can a Newby ASK to tour with someone???? A combination of things???