From the publisher:
A series of d20 race supplements from Silven Publishing utilizing the 3.5 rules set. Not simply a collection of elf and dwarf variants, the Races of Twilight series provides detailed information on unique and original player races that can be incorporated into any fantasy campaign. While intended for the experienced gamer who enjoys deep characterization and roleplaying over one-dimensional heroics and "roll-playing," Races of Twilight can be used by anyone who likes unusual characters.
Each of the races presented are in some way approaching the final phase of their cultural, political, or physiological development and are slowly fading from the world. Some have fallen into decadence and apathy; others have lost their dominance and position in a world of multiracial empires; still others have been crushed by disease, overpopulation, or magical travails. Whether each races dies and is forgotten or overcomes its difficulties and thrives is in the hands of players and DMs.
While each book provides numerous details on a new race, plenty of room is left for DMs to develop a unique background and role for that race in his or her campaign world.