The aim of the thesis is three fold: a-To develop a new questionnaire that measures anxiety in terms of four components (feeling, cognitive, behavior and somatic). b-To investigate the relationship between feeling and cognition with regard to anxiety. c-To identify, with the application of Three Systems Theory, the most salient component of anxiety in each of the DSM-III anxiety disorder sub-classifications and to evaluate the validity of DSM-III anxiety disorder sub-classifications. a-In order to assess the level of anxiety, I have developed a new Four Systems Anxiety Questionnaire (FSAQ). FSAQ incorporates a feeling component along with the behavioral, somatic and cognitive components. A psychometric evaluation (reliability and validity levels) of the questionnaire was found to be satisfactory. b-Another aim is to reconsider one of the tenets of cognitive therapy that cognitive appraisals are the necessary preconditions for the emergence of feeling. Such a view assumes that feeling is merely an epiphenomenon of cognitive processes. This research establishes, however, that feeling and cognition appear to be relatively independent systems and that their modes of interaction are influenced by the personality structure of the individual. This conclusion was obtained by using the FSAQ on university students and various categories of anxiety patients. In particular, the research compared the scores on the feeling and cognitive components of both males and females, obsessive-compulsives and rest of the DSM-III anxiety patients. c- A further aim of the reseach was to examine the DSM-III anxiety disorders classification from the Three Systems Theory's point of view. The Three Systems Theory proposes that anxiety has three relatively independent components: cognitive, behavioral and somatic. In the various anxiety sub-classifications of DSM-III one or other of these three components dominates. The other purpose of my research was to consider each of the DSM-III anxiety disorders separately and to determine which of the three components plays the major role in the manifestation of the particular syndrome. In general, the results indicate that each anxiety disorder is indeed characterised by a different profile. An anticipated outcome of this research is that a clinician will be able to identify the main component of anxiety in a particular syndrome and hence select most appropriate treatment. The results of this study support DSM-III classification of anxiety disorders into two main categories of phobic and non-phobic (i.e. phobic and anxiety states).