What is Compendium?

Before anything, the Compendium is the way Valve gives the community to participate in the grow of DotA 2. The compendium is a one time purchase and $2.5 of each compendium purchased is added to the prize pool of The International (the biggest yearly DotA 2 tournament), furthermore 25% of the money raised by points you can purchase to level your compendium up is also added to the prize pool.

The DotA 2 Compendium is a Virtual Booklet which bring features to its owner such as :

• Exclusive cosmetic items (For the hero but also : HUD, Taunt, Base personalization etc.)
• Lots of reward as more stretch goals are broken (currently the last 10M$ stretch goal was broken a few days ago)
• The ability to bet on the outcome of The International to compare your result with your friends
• Collect Pro Players Cards (just Like Pokemon Cards!)
• Play Challenges to increase your compendium level (Increasing your compendium level gives you even more rewards)
• XP booster (to drop cosmetic items more frequently when playing DotA)
• and much more...

This is by no mean mandatory and won't improve your ability to play. You won't play with a disadvantage by not having one but this is a nice feature to participate in the community.

The (current) compendium is an item related to the 2014 International DOTA 2 tournament.

It is a one time buy and does not provide any gameplay benefits to players.

Buying one raises the International price pool by $2.50, and leveling the compendium (by achieving objectives listed in the compendium) gives you increased battle points per match and new cosmetic items such as loading screens and hero items.