The study reported in this paper sought to identify reasons why teachers do or do not join unions. In addition, the study sought to disclose relationships between certain demographic characteristics and those reasons. The National Education Association/American Federation of Teachers (NEA/AFT) Membership Questionnaire, a Likert-type attitudinal survey with 16 items, was developed and responded to by 226 randomly selected certified teachers who were employed in a southern state. Data regarding grade level taught, years of teaching experience, age, gender, and political party affiliation were obtained as demographic variables. Of the 226 respondents, 88 belonged to the NEA, and 6 belonged to the AFT. Most of the teachers were females. Union members rated economic and psychological reasons as most important in their decision to join a union. Nonmembers cited social reasons for joining a union. The only demographic characteristic that was a significant predictor of whether a teacher would join a union was political party affiliation. The test instrument and tabulations of survey results are appended. (CB)