Since the world economic crisis of 2008 and governments' increasing demands for austerity in countries around the globe, labor unions have failed to provide leadership to the working class. This has led to a debate about the value of unions and their role in social change. Longstanding socialist organizations and emerging nonstate socialist and anarchist groups have begun an important discussion of the nature of the labor unions, the character of their leaderships, and their relationship to employers and the state. Marx and Engels are often referred to or cited as authorities in these debates, though seldom do we have an overview of how they arrived at their complex understanding of labor union structures, leaderships, politics, and behaviors. This essay is meant to contribute to this important discussion by examining Marx's and Engel's involvement in the workers' movement, including with the labor unions, as well as their writings about labor unions, placing them in the broader context of their revolutionary socialist strategy and vision. We trace the development of these ideas from their first involvement with the workers movement in the mid-1840s until the death of both by the 1890s. Finally, we conclude by making a summary of their considered opinion.