As in every field, paradigm shifts have occurred in the study of psychopathology and interventions for psychological disorders from time to time. Most people would agree that a paradigm shift occurred around 1980 perhaps best exemplified by the publication of the third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-III; American Psychiatric Association, 1980) with similar changes in the nosology of mental disorders appearing a few years later in the 10th edition of the International Classification of Diseases (ICD-10; World Health Organization, 1992). At that time conceptions and classification of these disorders largely shifted from a very global set of criteria based almost entirely on theoretical conceptions of psychopathology existing prior to 1980 to a more atheoretical empirically derived and more narrowly construed set of descriptors resulting in a marked increase in the total number of disorders. As with all paradigm shifts, the immediate result was a substantial surge in research on the nature and treatment of these new disorder categories. This research produced enough new information that two revisions to the DSM were deemed necessary within the space of the next 14 years, each with a further increase in the number of disorders, culminating in fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) published in 1994 (American Psychiatric Association, 1994). At that point many of the now hundreds of disorders specified could be to some extent identified reliably, and demonstrated at least some relationship to data on construct validity, origins, course, and treatment selection. Regarding the latter, this was particularly true for psychological treatments. After successful clinical trials requiring the operationalization of independent variables (interventions), many funded by government granting agencies, a large number of published manualized approaches to individual disorders such as panic disorder, major depressive disorder, eating disorders, and so forth appeared, many with supporting evidence (Barlow, Bullis, Comer, & Ametaj, 2013).These outcomes were seen by many, including many psychologists, as a positive and important step in the progression of knowledge in these areas since we now had for the most part reliable definitions of psychopathology that facilitated an active and robust program of research. With these definitions in hand, treatments, particularly psychological treatments but also to some extent drug treatments, could be developed and targeted very specifically to these disorders. This state of affairs represented something of a triumph for those working in the field of nosology and classification, who are often called splitters, referring to a preference for ever more narrow slices of psychopathology that can be identified in a highly reliable manner among clinicians, and a seeming defeat for lumpers who, as the label implies, believe that more valid approaches to classi- fying psychopathology requires focusing on commonalities and underlying dimensions.By the 1990s, and particularly after the publication of DSM-IV in 1994, most clinical scientists working in the area of psychopathology and classification observed that disadvantages had emerged as well from a splitting approach and that perhaps it was time to have another close look at overarching dimensions common across a number of disorders. It was also widely assumed that the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5; American Psychiatric Association, 2013) would almost certainly bring us well down the road to a more dimensional approach. One of the disadvantages of splitting had to do with the enthusiasm for publishing psychological treatment manuals. Once an initial manual was published for one disorder or another such as panic disorder, the incentives were lined up in terms of publishing contracts, additions to records of scholarly productivity, and other benefits such that variations on each manual began to appear from different authors. …