Near the end of the credits, just so there are no doubts: Catherine Zeta-Jones' singing and dancing performed by Catherine Zeta-Jones Renée Zellweger's singing and dancing performed by Renée Zellweger Richard Gere's singing and dancing performed by Richard Gere
There's no opening credits, save the title "CHICAGO".
The end credits are written in Broadway lights.
The title "CHICAGO" appears as a "C" in the middle of a zoom of Roxie's eye, then the rest of the letters light up around it.