When Civilization V
released nearly 2 years ago, it included a feature that allowed players to browse a list of community-created mods and install them directly inside the game. With the Gods & Kings
expansion pack on the horizon, 2K Games and Firaxis Games have decided to go a step further and overhaul the system to use Steam Workshop (and yes, this will be for the base game as well, not just the expansion!) See the full announcement here
Keep your eyes on the Steam Workshop
for the Civilization V update coming soon!