Bearded dragon are communal animals and can be housed together, though not all dragons will get along.
Males vs. Females
Do not house a male bearded dragon with another male. They are territorial animals and will fight. This fighting can cause stress or injuries to your beardies. Housing multiple females together is fine, as long as you have enough space for all the dragons involved. Too little space for too many dragons of any sex can cause stress, which leads to fighting for food and space. A 75-gallon tank is enough for two dragons, more than two will require a bigger enclosure.
One Male and Several Females
In addition to multiple females being housed together, one or several females may be housed with a single male, especially where mating is desired. Bearded dragon mating rituals are often violent and will involve the male biting the female on the tail, back and neck while in pursuit of her. To lessen this behavior, house one male with two or three females. Biting and fighting may still occur, but to a lesser degree.
Do not introduce bearded dragons until they are at least 18 months old; this is the minimum age for breeding. Housing them together sooner can lead one dragon to steal food and bully the other, which will often result in the male outpacing the female in growth and leaving her in poor health. When introducing bearded dragons, monitor their behavior carefully. If you can't keep a vigilant watch over them, house them separately until you can. While mild fighting is part of normal mating behavior, any fighting that draws blood or results in other injuries is cause for immediate separation. Some dragons just won't get along together. Don't force two hostile beardies into a single habitat.