This chapter asks: how can M. N. Roy's critical theory help us to understand fascism? Manabendra Nath Roy (1887–1954) was the founder of the Communist Parties of Mexico and India and a socialist-humanist philosopher. In the Western world, his works are today widely ignored and forgotten. This chapter introduces some philosophical aspects of Roy's thought. Frankfurt School thinkers such as Theodor W. Adorno, Max Horkheimer, Herbert Marcuse, and Erich Fromm were interested in similar topics as Roy. This chapter also compares the approach of Roy and the Frankfurt School. It shows parallels between Roy and the first generation of the Frankfurt School in respect to themes such as the dialectic of technology and society, the dialectic of the Enlightenment, fascism, nationalism, and authoritarianism. In the age of new nationalisms and authoritarian capitalism, global environmental crises, capitalist crisis, and the digital crisis, socialist-humanist theories such as the one by M. N. Roy can inspire struggles for a humanist and socialist society as antidotes to the acceleration and deepening of society's crises.