<p>The objective of this paper is to present a critical sustainability science research program, which is founded on two critical theoretical/philosophical traditions: critical realism and historical materialism. We elaborate these traditions to clarify what they can analytically offer to socioecological analyses in sustainability science and emphasize their prospective contributions to sustainability transitions and transformations. A critical sustainability science research program can facilitate bridging the natural and social sciences, provide crucial insights into social conditions and processes that drive ongoing and concerning environmental changes, identify—often underexplored—socioecological conditions for sustainability transitions/transformations, and reveal structural process that can advance or impede them. The critical sustainability science approach offers an alternative to both mainstream and (critical) idealist/culturalist approaches in sustainability research.</p>