In order to satisfy the increasingly enhanced requirements for system performance, practical engineering systems are now frequently modelled as complex interconnected systems. The study of such classes of systems is both challenging and adventurous due to the presence of nonlinearity, interconnections between subsystems, time delay and uncertainty between such models and the real world. The research described in this proposal aims to develop a novel design approach and to provide practical but rigorous solutions to the problems of decentralised observer and controller design for complex interconnected systems using HOSM techniques. The project will strengthen the collaboration between two leading sliding mode research teams to create a framework for this new research area. In order to avoid packet problems with transfer of information between subsystems, decentralised strategies will be the focus of this research. A novel approach involving artificial interconnections will be developed to reduce the conservatism caused by interaction between subsystems when decentralised strategies are employed. One specific focus will be to remove/suppress the undesired chattering to improve closed-loop system performance. The investigator has been heavily involved in research on interconnected systems using classical sliding mode control for over 10 years and has a strong research track record. The project partner has obtained excellent results in HOSM control specifically in chattering suppression, which is internationally leading in the area of HOSM. The expertise of both research teams is considerable and complementary. The experimental equipment provided by the projector partner will be crucial for testing the results obtained. All these factors are very important to guarantee the project success. As the focus of this proposal is to remove chattering whilst preserving the advantages of HOSM techniques and decentralised strategies, this research will bring the advantages of high robustness to uncertainty, ease of implementation, high reliability and increased lifespan of moving mechanical components when implemented in real systems. The research has great potential to enhance economic efficiency.