In the United States, the most common hedgehog offered as a pet is the African pygmy. It is not recommended to keep hedgehogs in groups as they can fight and injure or kill each other. However creating a group of hedgehogs is not impossible and can be accomplished if care is taken to prevent injury and stress to the animals.
If you try to keep multiple hedgehogs, the first strategy you can employ is to use a large cage so the animals do not feel crowded. Provide each hedgehog an area to hide in and preferably its own space in the cage. In addition to space, make sure there is plenty of food and water for the hedgehogs. This will help avoid fights over these resources if the animals feel they are in limited supply.
If you are going to group the hedgehogs, group females together. Males will more than likely fight and injure (or even kill) each other over territorial disputes. Females may fight as well, but they are more likely to tolerate another female hedgehog's presence. Male-female pairs can be formed if you plan on breeding the hedgehogs, and you can establish a harem by pairing three females with one male. If you elect this strategy, be prepared to raise the young.
How to Indroduce
Introduce hedgehogs to each other slowly. You can usually start by releasing both hedgehogs in an area they are unfamiliar with, such as a bedroom or living room. Make certain the room is safe for the animals and do not leave them unattended. Observe their interactions. If there is any fighting, you may want to reconsider housing them together. If the animals do not fight, you can slowly introduce them to each other in enclosed environments such as their cages. It is advisable to use a new cage to place the pair in so they do not identify it as their territory.
Identifying the Individuals
If your hedgehogs tolerate each other, then you should consider having a way to identify them. If their colouration is different, the colours will provide enough distinction. If they look the same, you may want to have a microchip inserted in the animals' tissue. This is particularly useful if one of the hedgehogs becomes ill and needs vet care.