Professor Threadgold guides us through the Footprint Fly system: he identifies the factors which attract a trout's attention as a natural fly drifts into its window and devises patterns which do just that. The patterns are refined aerodynamically so that they land the right way up and are intended to be tied successfully by any more or less passable fly tyer. They are also intended to form the beginnings of a larger family of patterns by easily allowing variation and evolution of the basic patterns using the same range of techniques and materials. The author follows in the tradition of Vincent Marinaro and Goddard and Clarke, but is chiefly concerned with learning from more purely academic research usually skipped over by fly fishermen.