Chapter 3 extends the algebraic parameter identification approach to a class of nonlinear systems where the vector of unknown parameters is weakly linearly identifiable. In general, the applicability of the algebraic approach for parameter identification is constrained to the availability of some of the state vector components. A restriction to be lifted towards the end of the book. Several examples of parameter identification in highly nonlinear systems are presented, including some actual laboratory implementation. The class of systems here treated include closed loop systems undergoing sliding motions, i.e., systems controlled by high frequency discontinuous bang-bang control inputs.