Well before the now flourishing field of animal studies, the thinkers associated with Frankfurt, Germany's Institute of Social Research theorized and problematized society's troubling relationship with animals. Early critical theory explored the various manifestations of "unrelenting exploitation" animals have experienced in human societies and maintained that the domination of animals is intimately linked to the domination of human beings, especially of women and racial and ethnic minorities. They criticized Western thought for instrumentalist attitudes toward animals and were committed to extending compassion to animals. Max Horkheimer, Theodor W. Adorno, and Herbert Marcuse mount four challenges to sociologists today: (1) to unmask the shared forms of domination experienced by both animals and marginalized human beings, (2) for environmental sociologists to make animals a principle subject of investigation, (3) for sociological animal studies scholars to engage with philosophy, and (4) to adopt a critical and normative sociological perspective when studying human-animal relations.