If you have a male betta, you can NOT keep them with other fish! They will fight to the death to defend their territory. You may be able to keep a small snail with him, and I've heard of people having success with keeping african dwarf frogs and male bettas together, but I've personally never tried it. You can keep bettas in a 1-gallon bowl (unheated and unfiltered) as the bare minimum, although they would probably appreciate a larger 2.5, 5, or 10 gallon tank. I wouldn't put them in anything much larger than that because he may freak out about the huge space and claim only a small corner of the tank, and it's an awful lot of tank for only one fish to maintain.
If you have a female betta, you can keep them with other female bettas and other small, non aggressive community type fish.
