This book considers proportional-integral-plus (PIP) control of non-linear systems defined by state-dependent parameter models, with particular emphasis on three practical demonstrators: a 1/5th-scale laboratory representation of an Lancaster University Computerized Intelligent Excavator (LUCIE), a full-scale (commercial) vibrolance system used for ground improvement on a construction site, and nonlinear ALSTOM Benchmark Challenge II. In each case, the system is represented using a quasi-linear State-Dependent Parameter (SDP) model structure, in which the parameters are functionally dependent on other variables in the system. The approach yields SDP¿PIP control algorithms with improved performance and robustness in comparison with conventional linear PIP control. In particular, the new approach better handles the large disturbances and other non-linearities typical in the application areas considered.