Modern is a constructed format that allows expansion sets, core sets, and Modern Horizons; from Eighth Edition forward, save for the Modern ban list. The modern format thus encompasses all cards that have been printed in a core or expansion set using the modern card frame (plus some others from Time Spiral).
Here are a list of Modern Legal Expansions. You can click them and it will take you to our collection of cards available for that particular expansion.
The following card sets are permitted in Modern tournaments: