The development of electrically heated converter (EHC) systems that combine heated and unheated core functions is discussed. This “cascade” converter approach provides for effective energy transfer between the electrically heated core and a small volume, unheated metallic core. Cascade-type EHC systems demonstrate improved cold start hydrocarbon emission performance in FTP vehicle tests, versus early EHC configurations which combined a small volume EHC with a large volume, main converter. Examples of the FTP emission performance of cascade-type EHC systems are presented for both low-mileage situations and after accelerated engine aging that simulates high-mileage applications. The design flexibility of current cascade-type EHC configurations is reviewed with emphasis on reduced electrical energy consumption and mechanical durability. Recent designs have been developed which combine both the heated and unheated cascade functions into a single metal core.