For the individuals experiencing them, delusions and strong beliefs can be profoundly distressing and extremely limiting to healthy living. They also present significant challenges to the mental health professionals working with these individuals—not least because there is not always consensus around what might be considered delusional. For the first time, Decoding Delusions gathers the literature and treatment guidance materials related to delusions in one place to offer clinicians an up-to-date, culturally informed, and illustrated guide to managing the spectrum of delusions and other extreme beliefs encountered in daily practice. In Part I, chapter authors define and assess delusions, examining the current research literature into their linguistic and cultural aspects, as well as the history of their treatment. Crucially, it also provides a lived-experience perspective. Part II features the insights of a series of international experts on interventions—including third-wave cognitive-behavioral models such as compassion-focused therapy—for delusional presentations that include the following: • Persecutory paranoia• Delusional jealousy• Erotomania• Capgras syndrome• Delusions of thought possession• Trauma as a pathway to delusions Readers also will find a nuanced discussion of working with patients from Japanese backgrounds that will enhance their cultural competency and encourage them to think about extreme beliefs through a cultural lens. In Part III, the chapter authors explore the management of delusions in specific settings. Examples include delusions in forensic settings and use of remote technologies such as Zoom and digital media for measurement-based care. Finally, live-action demonstrations of key clinical skills at work are provided through video clips. Unlike any other resource currently available, Decoding Delusions proposes an approach that supports the exploration of extreme beliefs with the aim not only of distress reduction but also meaningful recovery.