EVE Online: Odyssey 1.0 will be deployed on Tuesday, June 4 during an extended downtime. The downtime is scheduled to begin at 08:00 UTC and run until 13:40 UTC. This downtime will run longer than normal because Odyssey is bringing a number of changes to skills which require an extended time to deploy properly.
Odyssey is bringing a number of changes to EVE Online, including a complete revamp of the exploration mechanics, a new hacking minigame, tags for sec status, rebalancing of navy ships and battleships, dual character training, visual improvements, and much more.
Full patch notes are available here.