
In late 22nd century North America, a world-wide rabies-like pandemic caused by a mutated strain of rabies called Rabies Z has triggered a zombie apocalypse, especially in the world's megacities.

While it is a real-time strategy game, players can pause at any time in order to plan future actions and give simultaneous orders.

Much like the player has access to different unit types, zombie types are also varied, ranging between slow, decrepit ones, extremely fast zombies called "Harpies", highly-resistant ones known as "Butchers" and others, including a massive "infected giant" that has high health, speed, and damage that is also highlighted on a minimap, requiring the player to not only have a strong defensive perimeter (with walls, turrets, towers and traps), but also adapt tactics accordingly. The player must keep zombies from breaching base defenses and infecting non-defensive structures, especially in tight or overdeveloped areas where a domino effect outbreak can occur. Zombies will attack the player's base at random intervals in small numbers, and larger hordes will appear at set times over the course of gameplay, culminating in a very large "final horde". Structures and units, many of different variations and following a tech-tree, will require different materials to be made. There are eight resources that the player must manage: gold, food, workers, wood, stone, iron, oil, and energy. Infected villages, called Villages of Doom, can be pillaged for resources, although a backlash of zombie swarms can result. The player's goal is to build a base to protect themselves, by planning the layout and defenses, exploring the map, collecting resources and expanding while fighting the local zombie population at the same time.

They Are Billions pits the player in a randomly generated steampunk themed, zombie-infested world.

PlayStation 4 and Xbox One versions were published by BlitWorks on July 1, 2019. The game was released with a campaign titled "New Empire" on June 18, 2019. Available on Microsoft Windows, it was released onto Steam's Early Access program with a survival mode in December 2017. They Are Billions is a post-apocalyptic steampunk real-time strategy survival video game developed and published by Numantian Games.
