This chapter considers the context of nineteenth-century science—particularly galvanism and its investigations of the boundaries between life and death and its attempts to animate the dead—against its vital role in animating Mary Shelley’s Frankenstein. In so doing, it charts not only the nineteenth-century sciences of the “undead” that marked such a significant moment in the history of science but also their impact, via Frankenstein, on much of what we now consider essential aspects in tales of zombies and the undead even today. I conclude by considering the ways that Shelley’s morbid interest in the biological sciences of death and the undead, and the questions it raised about the possibility of a supernatural afterlife, vitally infuses her philosophy of a life which had been so marked by death. Concluding with her essay On Ghosts, and what it reveals about Shelley’s concepts of death and the body, this chapter traces the footsteps of the walking dead through Mary Shelley’s life and writing.