Scythe

A world with no hunger, no disease, no war, no misery: humanity has conquered all those things, and has even conquered death. Now Scythes are the only ones who can end life-and they are commanded to do so, in order to keep the size of the population under control.
Citra and Rowan are chosen to apprentice to a scythe-a role that neither wants. These teens must master the "art" of taking life, knowing that the consequence of failure could mean losing their own.
Scythe is the first novel of a thrilling new series by National Book Award-winning author Neal Shusterman in which Citra and Rowan learn that a perfect world comes only with a heavy price.