The document, part of a series of chapters described in SO 011 759, presents an overview of theories about the labor market structure, suggests hypotheses about patterns of job shifts, and describes methods and results of testing these hypotheses. Three sections comprise the document. Section I defines basic labor market terms. Section II considers alternative explanations of the dependence of job-shift patterns on labor market structure and reviews literature concerning flexible and inflexible employment conditions. Flexible conditions occur when an employer can readily adjust an employer's wage up or down and either employer or employee can terminate the match at any time, whereas inflexible conditions assume that employers cannot readily adjust an employer's wage or terminate employment. In this section the author also proposes a new model for analyzing job shift patterns. Section III discusses a study of job shift patterns for full time jobs of civilian nonagricultural male workers in the labor force in 1968. Job rewards (wages and prestige) and personal resources (education and ability) were the basic variables. Results indicate that the proportion of job shifts accompanied by gains in prestige and wages exceeds those accompanied by losses. The finding is consistent with the argument that employment tends to be more inflexible in large firms than in small ones, assuming that most intrafirm moves originate in large firms. Also, the effect of education on upward moves is greater for interfirm moves than for intrafirm moves. Finally, the results indicate that determinants of a job shift rate depend on a person's social location and not just on his characteristics. (Author/KC)