mined cognitive schema imposed on clinical an d scientific informatio n to increase its com-
prehensibility and utility. Not surprisingly, as th e foundational science that ultimately led
to DSM-III has approached a half-century in ag e, challenges have begun to emerge for cli-
nicians and scientists alike that are inherent in the DSM structure rather than in the de-
scription of any single disorder. These challenges include high rates of comorbidity within
and across DSM chapters, an exce ssive use of and need to rely on “not otherwise specified”
(NOS) criteria, and a growing inability to integrate DSM disorders with the results of ge-
netic studies and other scientific findings. 
As the APA and the WHO began to plan their respective revisions of the DSM and the
International Classification of Disorders  (ICD), both cons idered the possibility of improving
clinical utility (e.g., by helping to explain a pparent comorbidity) and facilitating scientific
investigation by rethinking the organizational structures of both publications in a linear
system designated by alphanume ric codes that sequence chap ters according to some ra-
tional and relational structure.  It was critical to both th e DSM-5 Task Force and the WHO
International Advisory Group on the revision  of the ICD-10 Section on Mental and Behav-
ioral Disorders that the revisions to the or ganization enhance clinical utility and remain
within the bounds of well-replicated scientific information. Although the need for reform
seemed apparent, it was import ant to respect the state of the science as well as the chal-
lenge that overly rapid change would pose for the clinical and research communities. In
that spirit, revision of the organization was approached as a conservative, evolutionary di-
agnostic reform that would be guided by emer ging scientific evidence on the relationships