A society is divided into 5 factions representing certain qualities - Dauntless the courageous, Candor the honest, Amity the peaceful, Erudite the intelligent, and Abnegation the selfless. Everyone lives their childhood according to those qualities of the faction they are born into. At 16 comes the life choice - to stay or change factions. (It sort of reminded me of Harry Potter and the sorting hat...)
The main character moves from her Abnegation faction to Dauntless - quite the shift! During her "testing" period is confronted with a lot of questions about herself, and ultimately the society as a whole. Can you really live your life totally selfless? Follow knowledge to the cost of everything else?
This is fast paced book and hard to put down.
BTW - This dystopian society is located in Chicago - imagine Lake Michigan as a marsh.