This paper reports some of the central findings of a cross-sectional analysis of determinants of trade union membership in West Germany. Representative surveys are available for the periods 1976 to 1979 and 1980 to 1984. The results of a logistic regression model are presented separately for each period. Size of firm, union membership of works councillors, and employment in public service were found to be important ‘context variable’ which influence an individual's propensity to join the union. Other variables such as sex, education, and politicalpartisanship (Green Party) also have a significant influence on trade union membership and are discussed here in detail