The short answer to your query (as is a standard response in the National Library's reference service) is "No, probably not." Let's look at this in more detail.

a) Other rabbits. There are several reasons why this probably won't work. Rabbits, especially does, are very territorial. Unless they have been raised with the other bunny or the other bunny was introduced within a week or so, they will reject, even attack the new rabbit. There are always exceptions to this (I had two does, both adult, one a Cashmere Lop born and bred in Canberra and the other, a Dwarf Lop, born and bred in Sydney introduced - their idea, not mine - when they were well over two years old who ran together and played together until the Dwarf Lop died. I also had a trio of rabbits, a desexed English-cross buck and two does, one Dwarf Lop and one Black Otter crossbreed who were introduced quite late but became the three musketeers until killed by a Malamute that got into the yard when they were out playing.)

Another consideration I have heard other breeders mention is that the solo rabbit will bond to you but if you introduce another rabbit and they do get on, they will bond to each other and you will no longer have a true pet. If, on the other hand, the rabbit is a show rabbit, something Gwen Parsons said to me once is equally applicable to rabbits as guinea pigs. "If it is good enough to be shown, treat it like a treasure. Don't put it with another [guinea pig] where there is any risk of damage." This is sage advice. Even if rabbits do get on, at least at first, they can turn on each other and inflict considerable damage to the ears especially, or in the form of small abscesses. Some of our breeders who also board rabbits have mentioned finding all sorts of scars and other wounds on the rabbits whose owners ran them with another rabbit.

b) Guinea-pigs. There are two schools of thought on this. One, led most vociferously by British guinea-pig fancier, Peter Gurney, is an emphatic "No." He has a point - guinea-pigs can be frightful bullies. The reasons given are that rabbits can inadvertently hurt guinea-pigs when they kick off with their big back feet or sit on them or try to mate with them; that guinea-pigs have different dietary requirements from rabbits in that, like humans, they cannot produce Vitamin C so must have a higher intake of vegetables than many rabbits will tolerate.

On the other hand, many people have kept the two together for years with no problems and found they get on just fine, especially if the rabbit house-mate is a Netherland Dwarf so not much bigger than the cavy. Even many cavy breeders only feed the piggies greens once a week so an excess of vegetables isn't a problem for the bunny. Besides, Peter's Rabbit & Guinea Pig mix (free plug here) contains added Vitamin C. The rabbit can often act as the guinea pig's protector - they will hide behind the bunny and let her take care of the threat (and can do, especially if a Lop).

It rather depends on the personality of the individuals involved. I had a guinea pig, Yuki, I put in with a Netherland Dwarf crossbreed and there was no problem. When I sold him, I put her in with another Neth and he bit her. Instead of running away as the book says they do, she bit him right back so there was a small white cavy with a hank of black rabbit fur in her mouth. I moved her temporarily to a cage with a black Dwarf Lop buck who was in disgrace for turning on Camilla, the Cashmere Lop and tearing her ears. Yuki, who couldn't have known about this, still made a pre-emptive strike - she'd obviously had it with black rabbits, whatever the breed. She bit his bum, then bailed him up and wouldn't let him in the hutch, though only a fraction of his size. (Camilla must have been gleeful - here was one creature Scipio couldn't bully.) Yet Yuki was very fond of another Dwarf Lop, a Marten Sable also named Scipio I put her in with later and used to cuddle up to him. Her companion, another sow, named Kiri, used to like to sleep on Camilla, though at one point it did seem that the hutch belonged to the two cavies as Scipio II used to roost on its roof.

c) Cats. Your own cat, if properly introduced and once it realises this is a member of the household - no problem. Sadly, rabbits don't always extend the same courtesy to the hapless cat. Mine took few prisoners when it came to the Siamese and the Oriental residents. A Lop used to chase the Oriental out of the yard regularly and generally terrorise him. My big black Rex relentlessly stalked the Siamese from the kitchen, to the laundry and back again and a Neth used to lead the Oriental a merry chase across the garden, laughing at him over his shoulder. Then there was the case of a friend's white Oriental cat who decided to visit the trio of large Rex rabbits she had in a run. The black buck sat on him and all you could see was a big black velvet bunny with some white fur protruding from beneath him. Having extricated himself from that, the unfortunate cat was seized by the doe, flung down and given a thorough bath. How humiliating.

Most of my rabbits tend to think a cat the best toy a bunny ever had.

That said, stray cats can be a real problem, especially to small rabbits, whether half-grown Mini-Rexes or Neths of any age. They tend to avoid larger rabbits like Dwarf or Cashmere Lops (a stray decided he'd investigate the open pen where two of my Lops were exercising - he'd killed two young Mini-Rexes the year before. As one, the Lops turned on him, coming up to the wire, leaning forward aggressively like two small dogs, their whole body language saying, "Step in here, whatever you are, and we'll rip you to shreds." The cat beat a retreat promptly.) Then there was the case of the cranky Lop doe whose pen was invaded by a stray cat. Said cat rapidly achieved sub-orbital flight courtesy of the doe's powerful back legs. And of course, the medium to large rabbits are even less of a problem (Satins, Rexes, etc.). Sometimes a larger rabbit will protect a smaller one as happened with a friend's desexed crossbreed buck who had hitherto taken no notice of a baby rabbit left with his owners to look after until a stray cat came creeping into the yard and stalked the baby. Suddenly the big buck was on the cat's back and raking it fore and aft with his claws. What was left of the cat fled over the fence.

If strays are a problem, and you keep your rabbits outside, make sure the locks on the cages are secure because cats can work them loose, depending on the type. The big metal hook that fits in an eye on top of the cage as is the case with the metal ones commonly available can't be opened as it is the wrong angle and too stiff. But the small hook and eye on the side of some wooden ones can easily be lifted by a cat but fortunately such a type can easily be fitted with a padlock. It is a good idea to cover the open part of the cages with flyscreen wire. Not only does this keep out disease-carrying insects but it prevents the cat from getting its paws inside and frightening the rabbit (which can be as fatal as if the cat actually caught it) or hooking out baby rabbits.

d) Dogs. As I have never owned a dog, I don't know how they go with rabbits, though I do know of one German Shepherd who was very attached to the pet Lop and when it died, he pined and pined and was very excited when they got another Lop. And I do know several of our breeders have dogs as well as rabbits. I have also heard of a Lop buck, who on being stalked by the family's Jack Russell, leaped on its back and bit the dog and of a Netherland Dwarf who launched herself at a St Bernard and bit his nose because he came to close to her nest.

Stray dogs are a real problem. They can tear open both wooden and even the metal outside hutches, something a cat isn't strong enough to do. Even if they don't attack the rabbit, just being picked up in the dog's mouth and then put down is enough to cause the bunny to die of shock and it can happen so quickly. The only thing, if dogs are likely to get in the yard is to make sure they can't. Fill in any gaps in the fence, make sure the yard gate is shut and too high to be jumped over, likewise the fences. Reinforce wooden hutches with heavy inch wire, move them inside a shed or garage during the day or when no one is at home. If you have rabbits in a shed, put a bolt on the door as dogs can push a sliding door open. Of course, this is all only necessary if you have stray dogs getting regularly into your yard.

So, to sum up: If you want your pet rabbit to bond to you as a true pet, don't worry about getting him/her a companion. However, if you feel happy to have him/her bond with another animal, you can try either a rabbit of the opposite sex (but desex the buck) or breed your bunny if she's a doe and keep one of her daughters with her. Or you can try a guinea pig, but in both cases keep an eye on the animals to make sure one doesn't turn on the other after a time and be prepared to separate them permanently into different cages. If you intend showing the animal, whether rabbit or guinea pig, house them separately to avoid torn ears and other wounds.