Diablo 3 - Season 3 End & Season 4 Start Dates

Season 3 End & Season 4 Start Dates:

There will be a short period of time between when a Season ends and the next begins. During this time, you’ll be able to sort through your rollover rewards and review your progress on the Leaderboards. It’s a great time to reflect on the accomplishments you’ve made and enjoy the culmination of your pre and post-Season loot hunts!

Season 3 will be ending at the following dates and times for each region:

    North America: Sunday, August 23 @ 5:00 p.m. PDT
    Europe: Sunday, August 23 @ 5:00 p.m. CEST
    Asia: Sunday, August 23 @ 5:00 p.m. KST

Season 4 will be starting shortly after at the following dates and times for each region:

    North America: Friday, August 28 @ 5:00 p.m. PDT
    Europe: Friday, August 28 @ 5:00 p.m. CEST
    Asia: Friday, August 28 @ 5:00 p.m. KST

SOURCE