The different chapters of this book cover a large range of information regarding electrical actuators, including: synchronous and asynchronous machine modeling in order to measure and identify offline and online parameters using modern optimization methods; identification in real time of parameters with Luenberger filter and the extended Kalman filter; estimation of non-measurable variables, first by linear estimates and observers, then by lower observers. Robustness is a very problematic issue, as well, which is fully explored in a chapter dedicated to the subject. Finally, the estimate of non-measurable mechanical variables is particularly dealt with: estimate of load moment, then observation of the positioning of a command without mechanical sensor. The conditions to measure variables and real implementation of numerical algorithms are also examined with particular attention.