Acts divide Path of Exile's storyline into sections. Each act has its own quests, town, NPCs and an act boss at the end.
Since The Fall of Oriath expansion, there have been ten acts broken into two parts, each part spanning a large arc within the storyline. New acts were generally added to the game with every major expansion until the release of the ten-act system.
See Wraeclast for more information
Each act takes about 12 months to complete depending on available development resources 
- Added Acts Five through Ten.
- Removed the Cruel and Merciless difficulty levels. Path of Exile is now a single ten-act playthrough.
- The Awakening introduces Path of Exile's fourth act, which is set in and around the mining town of Highgate, north of Sarn.
- Act Four contains 14 new areas to explore, 40 new monster varieties to fight, 6 new quests to complete and 9 new bosses to defeat!
- Highgate contains a cast of new NPCs that have full voice acting.
- Added six new world areas (in all three difficulty levels) across three new tilesets. There are three new quests.
- Added a grand finale boss fight.
(Editor's note: the zones Imperial Gardens, Hedge Maze, The Library, The Archives, The Sceptre of God, The upper Sceptre of God and the boss Dominus were added to Act 3 expanding it)
- The City of Sarn, Path of Exile's third act, is now available! It includes 21 areas based on 8 new tilesets, 18 completely new monster types and over 90 monster variations.
- Act 2 was added some time during the alpha for which patch notes are missing