This article investigates the metaphor of the epigenetic landscape as it is used by embryologist Conrad Waddington, in order to explain how gene regulation modulates cellular development. The author recapitulates Waddington’s theory of epigenesis, highlighting its foundation on the idea that genes respond to internal and external stimuli which, by activating or inhibiting their expression, are also able to modulate their activity. Throughout the paper, the author explains how Waddington successfully employed the metaphor of the epigenetic landscape, and also resorted to the image of marbles rolling down a hill as an adequate visual representation of the cellular development process, and therefore of the mutations that affect developmental anatomy.