Between 1956 and 1976, unions in the government sector increased their membership by more than 2 million. Reasons for changes in union strength range from catastrophes, such as war and depression, to changes in the occupational and industrial strength of the work force. The policy changes which occurred from 1956 to 1976 to encourage bargaining were probably no more important than several other factors in explaining workers' decisions to join bargaining organizations. Only for certain functions, such as higher education, was public policy the dominant influence on the growth of bargaining. There are many reasons why Federal workers join unions; one may be because the costs of joining are limited. Most workers can join without facing the prospect of going on strike and public policy requires Federal agencies and departments to be neutral during union organizing drives. In contrast, private-sector employers may make noncoercive arguments to persuade their employees not to join a union. The need for additional research on bargaining organizations is cited, and it is suggested that a theoretical model of the determinants of the extent of bargaining and membership in bargaining organizations be developed, followed by empirical examinations based upon the model. Tabular data and 40 bibliographic listings are provided.