Wither, by Lauren DeStefano

This won't be out until late March, but I was lucky enough to get an ARC of this- it was fantastic!!!!!
YA dystopia (surprise), with a polygamous twist. After scientists have used genetic engineering to eliminate cancer and most diseases, the first generation was healthy and long-lived- but after that, males die at 25, and females at 20. Desperate oligarchs have turned to polygamous marriage to try to keep family lines intact, and girls are kidnapped to become brides and childbearers, to widen the gene pool. Rhine, Jenna and Cecily have been brought as brides for Linden, a clueless and ineffectual aristoctrat.
The world-building in this was wonderful, and fully developed characters deepened the high-concept plot. Couldn't put this down, read it in one sitting.