Due to their cost and their reliability, multicellular converters are interesting devices to supply electrical systems in many applicative fields. The first part of this chapter deals with the controller design for switching power converters, which are a particular class of switched systems. Two controllers are introduced. The first one is based on the average model and exhibits good performances in the transient. The second one is based on a Lyapunov function to jointly control the load current and the capacitor voltages across each commutation cell while improving the steadystate behavior. The second part of this chapter deals with the observer design to solve the capacitor voltages estimation while taking into account the hybrid behavior of the converter. A hybrid observer, based on gathering partial information from individual modes of the switched system, is designed. Some simulations highlight the efficiency of the proposed control and observer schemes for the three-cells converter.