Switching systems are systems comprising a set of continuous dynamics orchestrated by a switching signal. The development of tools allowing analyze the dynamic properties such as controllability, observability is essential before any order design step. The objective of this book is to contribute on the study of the structural properties of switched linear systems. More precisely, we provide some significant results on the controllability and observability of switched linear systems using geometrical tools. In another work stream, we develop an observer design for planar switched systems based on the geometrical study of the observability. The theoretical results are applied on multicellular converter. We provide simple conditions on the observability of this converter as well as a new state observer based on information gathering. Simulation results show the efficiency of the obtained results.