Guide
Performing Rights Organizations: How to Join a PRO
How to join a performing rights organization, what a PRO collects, and why your songs earn nothing on the performance side until you have an IPI number.
In the US you can actually join two PROs: ASCAP or BMI. SESAC and GMR are invitation-only. You pick one. Membership is exclusive.
Join as a writer for free. Join as a publisher if you want the publisher's share of performance royalties — otherwise that half has nowhere to go, or it sits with whoever registered the publisher account.
The IPI number you receive is how every society on earth identifies you. Found Royalties needs it to file. Get it first, then add songs.