On his home page at Michigan Zald wrote that his research focused "on social movement theory, organizational theory, and on sociology as a science and a humanities". Zald made substantial contributions to the field of social movement research. The term social movement organization (SMO) entered the literature through the work of Zald and Roberta Ash (now Garner) (Zald, Mayer N. and Roberta Ash, "Social Movement Organizations: Growth, Decay and Change." Social Forces 44:327-341, 1966). As of 2012 their article in "Social Forces" was one of top 10 most frequently cited articles ever published in this journal. With John D. McCarthy, Zald developed the resource mobilization theory, which became one of the major theories on social movements. Zald’s article with McCarthy, “Resource Mobilization and Social Movements: A Partial Theory,” published in the "American Journal of Sociology" in May 1977, has been described by Jeff Goodwin as one of the most influential and frequently cited articles in the field and in the discipline. Zald and McCarthy called "attention to the rising trend of professional activism in social movements and general principles of organizational dynamics to" social movement organizations.