In this paper, I address Max Delbrück’s conceptual and experimental importance for molecular biology (henceforth MB) origins. In particular, his complementarity approach and its anti-reductive implications on the (epistemic) reductionism debate in MB. Regarding Delbrück’s conceptual and experimental importance, I examine his influence on the development of MB by exploring a shift of his interests from physics to biology. Particularly, I outline his central role in “The Phage Group”, the informal group of scientists examining the origin of hereditary life using bacteriophages as their experimental model of choice. Delbrück and “The Phage Group” greatly influenced the development of MB, which culminated with the shared 1969 Nobel Prize for the discoveries regarding replication mechanism and genetic structure of viruses. Moreover, I examine Delbrück’s complementarity approach towards biological explanations. The complementarity in biology assumes that “biological phenomena might require the employment of descriptions that are mutually exclusive yet jointly necessary for understanding life processes” (McKaughan 2011, p. 11). I explore Delbrück’s complementarity approach, in particular the debate between the reductive and anti-reductive interpretations of it. I argue for the latter interpretation by suggesting that Delbrück advanced an anti-reductive view towards biological explanations by advocating for independent status of explanations of various biological disciplines. Furthermore, I address the complementarity approach in the light of the anti-reductive interpretation in the recent developments in MB, particularly, the potentiality of finding the complementarity approach in systems biology, epigenetics, and boundary selection.