Diel vertical migration (DVM) refers to the daily, synchronized movement of marine animals between the surface and deep layers of the open ocean. This behavior is the largest animal migration on the planet and is undertaken every single day by trillions of animals in every ocean. Like a big game of hide and seek, animals that perform DVM spend the day hiding from predators in the deep ocean, and then migrate to the surface to feed under the cover of darkness. In this article we will explore this incredible strategy for survival. We will introduce the animals involved, describe how the environment of the open ocean drives DVM across the globe, and hint at the questions still to be answered as the ocean environment continues to change.