When behavior therapy was first applied to what would now be labeled an anxiety disorder, a simplistic theoretical model guided the treatment of a sim ple phobia. Time and research have shown that the techniques of behavior ther apy have been more successful than its models have been explanatory. Yet progress has been substantial in both realms, as the following volume makes patently clear. In 1980 an inventory of this progress was catalogued at an NIMH-sponsored workshop. What both that workshop and this volume clearly show is that the behav ior therapy researcher need no longer suffer the epithet "overly simplistic." One of the major strengths of this volume is its elucidation of the complexities that now attend the study of the anxiety disorders, particularly from a behav ioral point of view. The researcher at times appears almost to be buried in a landslide of complexities regarding this topic. The concept of anxiety itself has undergone a differentiation to a level of complexity that poses problems for both the conceptualization and the treat ment of anxiety disorders. In virtually one voice, the several authors of this volume argue the multidimensional nature of anxiety. The "lump" view of anx iety has given way to the three-channel view of anxiety. An investigator's future research career could well be secured just by spending time puzzling out the significance of the low intercorrelations among the channels.