Cognitive Behavioural Therapy (CBT) is the treatment of choice for most mental health problems. Each different problem is usually treated by a different model of CBT. Yet evidence tells us that the same processes are responsible for long term distress in us all. This handy manual draws on evidence and theory to provide the key principles to aid change and recovery. The transdiagnostic approach is supported by a wealth of evidence that processes such as worry, emotion suppression, self-criticism and avoidance maintain distress across psychological disorders. Perceptual Control Theory (PCT) explains all of these processes as forms of ‘inflexible control’, and Method of Levels Therapy (MOL) helps people to let go of these habits. The principles and techniques of MOL are clearly and practically described for clinicians to offer a transdiagnostic CBT that is tailor-made to the goals of each client. This novel volume will be essential reading for novice and experienced CBT therapists, as well as counsellors and psychotherapists. Its accessible explanation of Perceptual Control Theory and its application to real world problems also makes a useful resource for undergraduates, graduates and researchers in psychology.