Modern technological systems consist of many components with strong interactions between them. Therefore, accurate and timely detection of faults can prevent the spread of them in the whole system and loss of effectiveness. On the other hand a broad category of modern systems have switching behavior and there are sudden changes in their continuous dynamics as a result of working in different phases or controlling them with discrete logic. Hence the problem of detecting faults in hybrid systems and in particular switching systems, has recently attracted the attention of researchers. In this thesis three problems in the field of fault detection that has received less attention for switched systems are investigated and solved. The first problem is isolation of faults in switched systems. Although many works have been done for isolating faults in linear and nonlinear systems, isolation of faults in switched systems has not been considered as much. To solve this problem, by selecting one of isolating methods in linear systems, named geometric approach, this method has been used to isolate faults in switched systems. For this purpose, by generalizing the notion of unobservability suace in linear systems to switched systems, an algorithm is presented to find it. Furthermore, using linear matrix inequalities (LMI’s) the gain of fault detection filter is designed so that in addition to stability, the effect of disturbances on the residual signal is reduced and at the same time the effect of fault on the residual is increased. Another issue that has been studied in this thesis is designing fault detection filter for switched systems in which the filter receives the switching signal with delay. For this purpose the stability condition with weighted erformance for asynchronous fault detection filter is achieved at first. Then these conditions are converted to matrix inequalities and by choosing special structures for unknown variables these inequalities become LMI’s. Using these LMI’s the filters are designed so that the residual is robust against disturbances and sensitive to faults. The last issue that is investigated in this thesis is simoltanious fault detection and control for switched systems. Using the LMI’s, obtained for stability and weighted erformance of switched systems in previous sections, a single block is designed for the purpose of fault detection and control. In the design of this block some nonlinear terms appear that can not be removed as easily as the previous problems. Thus more complicated change of variables and congruence transformations are used in this case. To show the effectiveness of the methods they are used to detect faults in a three-tank system. Key words : Fault Detection, Fault Isolation, Switched linear systems, Asynchronous Switching, Simoltanious Fault detection and control, Linear Matrix Inequality