When you create a character in Path of Exile, you choose a league for that character to exist in. We expect and encourage most players to play in the default league, but other leagues exist for specific play styles or events.
Characters can only see and interact with other characters in the same league. In this way, each one is its own isolated economy. The default league is extremely large and hence acts as a general economy for all characters that were not created in a specialist league. All characters in a league have access to the same shared stash pages.
Each league has its own set of ladder rankings. We’ll be frequently creating short term leagues that last varying durations (a day, a weekend, a week, etc) with item rewards for the highest placed characters on the ladder at the end of the league. There are leagues that end once a specific goal has been met (a race to level 90, for example).
League competitions are another way for players to get rewarded for their play skill and to be competitive with other players as an alternative to PvP.
There are a few permanent long term leagues including the default “standard” and “hardcore” leagues. All other leagues have a duration value and a parent league. When the duration is over, all characters in that league become part of the parent league.
Whenever any league ends, its characters are all converted back to its parent league. This way, no one loses the character they were leveling (it just ends up in a less restricted economy/ladder than the one it was initially being played in).
Leagues are able to apply a different set of game rules to their players. For example, increased monster difficulty, world PvP, permadeath or various "Ironman" rules.
We have many plans for interesting game modifiers that leagues can apply, but one rule is clear – they must only make the game harder. Because characters transfer back to the parent league when a league ends, it is important that the character’s journey to its current status was equivalent or more difficult than gameplay in the parent league.
In addition, we plan to allow guilds or groups of players to pay for the creation of their own league with a choice of game rule modifiers. Only players invited by the people who paid for the league can create characters in these private leagues. This option helps cater towards any groups of players who want to play online together but don’t want their playgroup to have access to items traded from external players.