Introduction -- Modelling for Fault Diagnosis -- Observer-Based Residual Generation -- Robust Residual Generation Based on Unknown Input Observer -- Optimal Robust Residual Generation -- Residual Evaluation Based on Threshold Computation -- Fault Isolation Based on Structured Residual Generation -- Fault Isolation Based on Directional Residual Generation -- Observer-Based Fault Estimation -- Kalman Filter-Based Fault Diagnosis -- Parity Space Approaches.