In this paper, we present a review of the recent advances in hybrid vehicle powertrain architectural design. The paper begins with a discussion and categorization of the various types of hybrid vehicles. The current leading technology is the one-mode design of the Toyota Hybrid System and the intent of the state-of-the-art architectures is to improve upon the perceived weakness of the one-mode design. The proposed designs employ multi-regime architectures that allow for the transmission to operate in any one of series, parallel, or power-split configurations, depending upon the road load, driver demand, and control strategy. These new designs found in the literature are discussed and compared. The work allows further study and detailed modelling of the promising multi-regime architectures to be carried out.