Guinea Pigs are sociable and therefore best provided with company, especially if the owner is away during the day or the guinea pig is to be kept outside.
Male guinea pigs (boars) kept together will most often fight once sexually mature, although neutered boars will live happily together. Female guinea pigs (sows) will also live happily together if introduced at a young age or carefully introduced at an older age. A boar and sow should not kept together as this will result in continuous breeding. Even if the intention is to breed at some point, the boar and sow should only be introduced for a short period for mating to occur and kept separate at other times.
Although guinea pigs and rabbits will "accept" each other as companions, the habit of a rabbit to playfully jump when happy means that its powerful hind legs can cause serious internal injury by mistake to a guinea pig companion, that could result in death. This is the case with even the smallest of rabbit breeds. Rabbits and guinea pigs also have different dietary requirements and different means of communicating. Therefore guinea pigs should not be housed with rabbits and the best and most natural companion for any pet guinea pig is always another guinea pig. | 
