Holland influenced practice and research in career development by contributing a clear theory useful in organizing information about individuals and career alternatives and for understanding individuals' entry and persistence in occupational and other environments. His theory was repeatedly revised in response to evidence. As Holland's own career unfolded in a succession of organizational environments, he used the research opportunities these environments afforded to conduct large-sample tests of his ideas and assessment tools. J. L. Holland's (1970) Self-Directed Search is intended to be a career intervention, and Holland developed it and tested it as such. In outlining Holland's contributions to career counseling, a precis of his theory and some biographical context are provided.