This paper presents and discusses a conceptual model for understanding, describing, and explaining personnel selection processes and activities. Four theoretical strands--decision theory, impression formation, inference theory, and rating theory--are briefly discussed and woven together as the basis for the proposed model. The model is then used as a theoretical framework for examining the results of a study investigating the effects of letters of recommendation on teacher selection processes and decisions. The study involved creating a file for a hypothetical social studies teacher that included one of four constructed letters of recommendation. The four letters each contained nine identical items of information about the candidate but varied by tone of information (favorable or neutral) and length of letter (short or long). Four treatment groups were established by sending the different types of letters of recommendation to 160 randomly selected high school principals in a large midwestern state. Major conclusions reached from the study are that when the content items of letters remain constant, there is no statistically significant difference in rating of teaching applicants who present long or short letters of recommendation. However, favorable information had a significant effect on the rating high school principals gave a hypothetical teaching candidate. (MLF)