Synthesis of a sequence of test signals for a rather complex analog circuit is a serious professional challenge which is mainly related to the difficulties to ensure both controllability and observability of the fault. Usually, attempts are made to use alternatively the DC, frequency, and time domain so exploiting the specific properties of the circuit. To do that, in this chapter we introduce several concepts including correlation of the time domain responses, multifrequency analysis, and most frequently DC studies. All these will be elaborated and exemplified in the next. In addition, attention will be paid to the testing economics, i.e., to find tests that need simple equipment, need less time to be implemented, and (possibly) cover as many faults as possible. An algorithm for creation of an optimal testing sequence will be described too.