Civilization V is to come with mod and editing tools, as well as having the ability to import maps from Civilization IV.
BigDownload spoke to designer Jon Shafer on the subject at E3.
"You can import Civ IV maps into the world builder and convert them into Civ V maps, including all the units and cities and stuff on it," he said.
Users will not be able to import total conversion mods which have custom art and designs, however the developer's expecting to see most of these remade for Civilization V when it's released in September.
It was also reported today that the anticipated strategy title will ship with basic multiplayer, with new modes to be added after the fact.