An artificial fly or fly lure is a type of fishing lure, usually used in the sport of fly fishing (although they may also be used in other forms of angling). In general, artificial flies are an imitation of aquatic insects that are natural food of the target fish species the fly fishers try to catch. Artificial flies are constructed by fly tying, in which furs, feathers, thread or any of very many other materials are tied onto a fish hook.

Artificial flies may be constructed to represent all manner of potential preys to freshwater and saltwater fish, including aquatic and terrestrial insects, crustaceans, worms, spawn, small baitfish, reptiles, amphibians, mammals and even birds. Effective artificial fly patterns are said to be killing flies because of their ability to put fish in the creel for the fly fisher. There are thousands of artificial fly patterns, many of them with descriptive and often idiosyncratic names.

Fly tying is a common practice in fly fishing, considered by many anglers an important part of the fly fishing experience. Many fly fishers tie their own flies, either following patterns in books, natural insect examples, or using their own imagination. The technique involves attaching small pieces of feathers, animal fur, and other materials onto a hook in order to make it attractive to fish. This is made by wrapping thread tightly around the hook and tying on the desired materials. A fly is sized by the size hook it is tied on. The construction of tube flies is different in that the tier secures materials to a tube rather than to a hook. These flies are rigged by passing the fishing line through the tube before attaching a hook.

Generally, fly patterns are considered either "imitations" or "attractors". These can be further broken down into nymphs, terrestrials, dry flies, eggs, scuds, and streamers. Imitations seek to deceive fish through the lifelike imitation of insects on which the fish may feed. Imitations do not always have to be precisely realistic in appearance; they may derive their lifelike qualities when their fur or feathers are immersed in water and allowed to move in the current. Attractors, which are often brightly colored, seek to draw a strike by arousing an aggression response in the fish. Famous attractors are the Stimulator and Royal Wulff flies.

The first literary reference to flies and fishing with flies was in Ælian's Natural History probably written about 200 A.D. That work discussed a Macedonian fly. The Treatyse on Fysshynge with an Angle was published (1496) within The Boke of St. Albans attributed to Dame Juliana Berners. The book contains, along with instructions on rod, line and hook making, dressings for different flies to use at different times of the year. Probably the first use of the term Artificial fly came in Izaac Walton's The Compleat Angler (1653),

Oh my good Master, this morning walk has been spent to my great pleasure and wonder: but I pray, when shall I have your direction how to make Artificial flyes, like to those that the Trout loves best?

The 1652 4th edition of John Dennys's The Secrets of Angling, first published in 1613, contains the first known illustration of an artificial fly.

By the early 19th century, the term artificial fly was being routinely used in angling literature much like this representative quote from Thomas Best's A Concise Treatise on the Art of Angling (1807) to refer to all types of flies used by fly fishers.