The brown is a native of Europe; several strains of brown trout have become established here in the United States and they are our most common salmonid. The Brown Trout is the Carp of the coldwater streams, having dominated almost every ecosystem they have invaded. These exotic fish have thrived in many streams rendered inhospitable to native brook trout by siltation, pollution, and damming. The typical brown trout is about a foot long and half a pound, although stream browns up to 31 inches long have been caught, and some migratory strains exceed even this. They are highly voracious predators, especially once they reach adult size. Browns are buttery-yellow or yellowish-brown in color, and covered in black and red spots of varying sizes.

Brown trout live in streams as well as lakes, where they are able to survive by migrating into adjoining rivers to spawn. They spawn in the fall, like the brook trout, and are able to displace spawning brook trout due to their larger size and aggressive behavior. Browns do well in hardwater streams with abundant insect life, but can survive in freestone streams and marginal habitat by feeding on crayfish, minnows, and suckers.

Browns often selectively feed on certain types of insects, both at the surface of the water and below it, and any serious student of the brown trout is very familiar with the mayflies, stoneflies, midges, and caddis upon which brown trout so often feed. Large browns often become "cannibals", eating not only smaller trout, but also crayfish, minnows, suckers, mice, and whatever else the stream might have living in it. Some populations of browns are anadramous, like the steelhead, and grow huge. In most cases, the best tactic for going after browns is with a dry or sunken fly on a lightweight flyrod. Brown trout are famous for their selectivity; during heavy hatches of one particular type of insect, they will gorge themselves on that exact bug and ignore everything else, no matter how tempting it might be. But it takes a very heavy hatch to bring out this behavior in browns, so most of the time generic "buggy" flies will produce plenty of them.