In Creatures, a user hatches small furry creatures called Norns into a world called Albia, and teaches them how to talk, feed themselves, and protect themselves against vicious creatures called Grendels. Later games in the series introduced a third species, the Ettin. They are white, red-eyed creatures that steal tools.

The program was significant as it was one of the first commercial titles to code alife organisms from the genetic level upwards using a sophisticated biochemistry and neural network brains. This meant that the Norns and their DNA could develop and "evolve" in increasingly diverse ways, unpredicted by the makers. By breeding certain Norns with others, some traits could be passed on to following generations. Most interestingly, the Norns turned out to behave similarly to living creatures. This was seen as an important insight into how real world organisms may function and evolve. Earlier alife programs had worked by giving their organisms a limited set of commands and parameters, and seeing whether the way the subjects behaved was realistic.

While this is the first commercial program it is to be noted that other non-commercial programs had done this since the late 1970s such as the Savanna Simulator by Walter Vose Jeffries which ran on an Z80 based Exidy Sorcerer microcomputer and presented the creatures moving on a graphical grid.

The genetics in Creatures are somewhat different from human genetics; they are haploid. There is no concept of dominant gene and recessive gene, much less recombination between loci. Nevertheless, the complexity of the simulated biochemistry meant that Norn behavior was highly unpredictable.

Among the fans of Creatures were the Oxford zoologist Richard Dawkins and author Douglas Adams.