From WotC:
This fall, Magic: The Gathering fans will return to the most revered plane in the Multiverse – Ravnica, a world covered entirely by city and ruled over by ten powerful Guilds. On October 5th, the Return to Ravnica set will kick off an exciting new block featuring the ten Guilds and will reveal new conspiracies and schemes that threaten to shake the foundations of the world.
In preparation for the return to Ravnica, players can visit Guilds of Ravnica where they will learn more about the ten Guilds and take a quiz to help them select a Guild to affiliate with. By affiliating with a Guild, players can take part in the battle for control of Ravnica and even earn Planeswalker Points towards their Guild by participating in Magic events at their local game stores.
Fans of Magic: The Gathering on Facebook can join in the action with the recently-launched Artfight: Ravnica game app, an interactive experience that allows players to compete for glory and influence over the plane and receive points to unlock unique gallery art and even preview an upcoming card.
