This collection of papers, concerned with the nature and theory of intelligence, forms part of a project to integrate test and factor theory with the empirical, functional relationships involving standard intelligence tests. The project will render more objective the use of factor analysis in personnel research. A definition of intelligence encompassing biological and socio-psychological factors is formulated in "Theory of Intelligence." Three classes of hypothesis are presented in "Hypothesis Developed From the Theory." In "The Psychological Test" a psychological theory is delineated as a basis for developing a theory of intelligence congruent with the experimental and observational correlates of measures of intelligence. Interrelations of homogeneity, reliability, and validity are considered in the paper of this name. "Illustrations of Test Characteristics by Means of Physical Analogues,""Evaluating the Importance of Factors in any Given Order of Factoring," and a description of "The Scottish Survey of Intelligence" complete the collection. (Author/CK)