From the publisher's website:
This 7 Wonders expansion allows to lead your civilization with great personalities: the leaders. Represented by 36 new cards, they will influence your city development. The course of play is slightly modified, but the victory conditions are unchanged. At the beginning of an age, each player chooses one of their leaders to play as a regular structure card. Then, the normal course of play resumes. These leaders can give victory points, scientific symbols, shields, cost reduction for playing cards, etc. These new cards bring new ways of playing, transforming considerably your games.