Divergent - by Veronica Roth (1st Book)

Paperback. Tris Prior lives in a futuristic world in which society is divided into five factions. As each person enters adulthood, he or she must choose a faction and commit to it for life. Tris chooses Dauntless -- those who pursue bravery above all else. However, her initiation leads to the discovery that she is a Divergent and will never be able to fit into just one faction. Warned that she must conceal her status, Tris uncovers a looming war which threatens everyone she loves.