Part 1 of the paper reviews four categories of protein fibers. (1) Wool and other hairs, which have been used as textiles for thousands of years. (2) Regenerated protein fibers, which were manufactured in the 1950s but did not achieve continued commercial success, and, in the 1990s, fibers from artificially produced spider silk proteins. (3) Hagfish slime threads, as an example of other biological fibers. (4) Silks, from silkworms and spiders. In Part 2, stress-strain curves are compared and discussed in relation to what is known of the structure of the fibers and the mode of formation. Models of the structural mechanics are described. The possibilities for scientific and commercial advances in future are presented in Part 3.