Getting a good seat at the theater is often expensive. Depending on the venue you're in, gold squares and first-class seats can cost from €30 to over €100, and it's not always easy for young people to take advantage of this. However, there are many theaters where under-26s (or even under-28s) can get good seats at the very low price of €10. These are private theaters belonging to ASTP (association pour le soutien du théâtre privé). There are over a hundred throughout Paris, but you can find a selection of the most popular theaters with the best programming below.
Note that the national theaters(Comédie française, La Colline, Odéon, Chaillot) also have a reduced rate for young people, but at a different price. As a general rule, it's always possible to find discounted theater tickets if you show up an hour before the show starts.
