Federal copyright law requires you to secure the proper licensing rights to play music at events.  

Helpful links:

• Top 10 Music Licensing Questions: How to Play Legal Music in Your Business. Cloud Cover Music.
• Why Pandora for Business. Pandora for Business.
• Music to Match Your Business Goals. Cloud Cover Music.
• Licensed Music for Business. Pandora for Business.
• What Are Music Publishing Revenue Streams? Houston Chronicle.