Rats usually live in packs, although there's little evidence of sufficient cooperation or division of labor to characterize them as truly social animals.

Adult male rats are territorial and will often chase away other males with aggressive posturing, shrieking, and other behaviors. Much has been written about Alpha, Beta, and Gamma rats, which supposedly represent three levels of dominance of males in a rat pack (with Alpha's being the most dominant). Because much of this research was conducted under artificial conditions, it's questionable how well it actually represents wild rat behavior. In the wild, territoriality and dominance among males seems more a function of age and size than of any particular "personality" traits.

Norway rats are also xenophobic, which means that they are cautious about new objects in their environment and tend to avoid them for several days. This has important implications for rat control because as rats typically will avoid traps or bait stations for several days after they are placed, and will permanently avoid them if their first contact resulted in sickness or narrowly escaping disaster in a trap.