Integrated hybrid transmissions serve as the key component in hybrid electric vehicles (HEVs). This paper reviews several technologies of the electromechanical integration of advanced hybrid transmission systems. Detailed configurations, fundamentals of operating principles, and various operating modes were comprehensively explained and analyzed. Combining the merits, an integrated electromechanical double-rotor compound hybrid transmission that is potentially more compact and has better performance is proposed. Detailed operation modes are compared, and functions and cooperation between integrated components are illustrated. As the core component of the integrated transmission, the double-rotor electric machine is studied via drive-cycle analyses, and a scaled-down prototype is built according to the drive-cycle analysis results. Test results successfully validate the design and simulation process.