In both DCTs and new ATs, the change of the speed ratio is regarded as the process of one clutch being engaged with the other being disengaged, namely, the clutch-to-clutch shift. For vehicles with a hydraulic cylinder as clutch actuator, the cylinder pressure control is important for good shift quality. Sensors measuring the clutch cylinder pressure, however, are seldom used in ATs because of the cost and durability. In this chapter, the design of reduced-order clutch pressure observers is discussed in the framework of input-to-state stability. Lookup tables, which are widely used to represent complex nonlinear characteristics of engine systems, appear in their original form. Model uncertainties including steady state error and unmodelled dynamics are considered as additive disturbances and the observers are designed in order that the error dynamics is robust stable.