Fly tying is the process of producing an artificial fly to be used by anglers to catch fish via means of fly fishing. Probably the most concise description of fly tying is the one by Helen Shaw, a preeminent American professional fly tyer in Fly-Tying.

"Fly-tying is a simple process of binding various materials to a hook with thread.".

Many fly-tyers consider fly tying an art, such as E. C. Gregg in introduction to How To Tie Flies.

"The object of this book will be throughout its entirety to teach in a practical manner the Art of Fly Tying in all its branches.”

At the other end is the apparent view of A. K. Best, a well known professional fly tyer and writer whose book, Production Fly Tying, suggests practical ways to streamline tying technique. Best emphasizes that fly tying is also a science rooted in careful observation of fish and their prey, and then designing and tying artificial flies to replicate that prey to catch fish. One of the first and foremost of these efforts was by Preston Jennings, in his classic: A Book of Trout Flies.

Fly tying requires some basic equipment, the appropriate materials for the fly pattern being tied and a fly pattern to follow or replicate. Fly tying equipment enables the fly tyer to efficiently and effectively assemble and secure the materials on the hook. Flying materials were originally limited to various furs, feathers, threads and hooks. Today there many different types of natural and synthetic materials used to tie flies. Fly patterns represent the “recipe” required to create the fly--what hook size(s) types to use, what materials are to be used, what colors, in what sequence and by what methods are they assembled on the hook. These are the elements of fly patterns. Of patterns, there are thousands.

Hand-tied flies on the commercial market retail from less than a dollar to several dollars each. Fly tying is a challenging and rewarding hobby for some, a money-saving strategy for some fly fishermen, and a profitable commercial enterprise for the professional tyer. The professional, commercial fly tyer may produce upwards 3000 dozen flies annually, whereas the amateur fly tyer may tie only a few flies each season for personal use.