The reaction of rhodium‐bound carbenes with strained bicyclic methylene aziridines results in a formal 3+1 ring expansion to yield highly substituted methylene azetidines with excellent regio‐ and stereoselectivity. The reaction appears to proceed through an ylide‐type mechanism, where the unique strain and structure of the methylene aziridine promotes a ring‐opening/ring‐closing cascade that efficiently transfers chirality from substrate to product. The resultant products can be elaborated into new azetidine scaffolds containing vicinal tertiary‐quaternary and even quaternary‐quaternary stereocenters. A tale of two rings: A one carbon ring expansion of methylene aziridines to methylene azetidines occurs upon reaction with a rhodium‐bound carbene. This 3+1 ring expansion efficiently delivers substituted azetidines in high yields and stereoselectivities.