Ragnarok Online will host events in game for players to explore and enjoy.

The following events occurs every year in a specific month:

• January:
  • New Year Event
• February:
  • Sweets Fair
• March:
  • Happy Egg Festival
• April:
  • Arbor Day
  • Spring Flower Festival
• May:
  • Melon Festival
• June:
  • Popcorn Festa
• July:
  • July Noodle Festival
• August:
  • Dimensional Rift
• September:
  • Thanksgiving Event
• October:
  • Halloween Event
• November:
  • Royal Hunting Event
• December:
  • Snow Festival

The following events occurs every month in a specific day:

• 10th Day at 21:00 Korean Time: Find the Lost Poring
• 17th Day at 22:00 Korean Time: Hugel Monster Invasion
• 28th Day at 22:00 Korean Time: Find the King's Mark

The following events may occur multiple times a year:

• Booster Promotion
• Kachua Diamond Exchange
• Ragmarble

The following events are permanently implemented and are always enabled:

• Web Vending Machine
• Event Stone Coin

The following events used to be implemented, but no longer hosted:

• Card Exchange
• RAG★FES

Sources:
https://gall.dcinside.com/mgallery/board/view/?id=ragminor&no=1647
https://www.inven.co.kr/board/ro/1951/5217