Molecular fundamentals of spider silk are protein fibers made out of the combination of aminoacids. Polypeptide chains that contain lots of different aminoacids create threedimensional structures until we get the silk which vary in its composition. Every single kind of silk gland produce a different kind of silk and, depending on the species of spider, the total number of silk glands may vary. Evolutionary origins of silk glands are still not completely examined. Because of the ectodermal origin of the silk glands, it's hard to say whether they developed from the coxal glands, which origin is mesodermal, or they appeared de nuovo. Inside of silk glands the protein liquid is being produced which, under the pressure, travels to the spinnerets. Spinnerets are placed on the surface of abdomen and while the protein liquid is being released, the liquid becomes solid, turning into the threads of a spider silk. Spiders are not the only animals that have the ability to produce silk but the reason why they are the most important silk procuders is because of their diversity of silk use and the fact that only spiders have special organs created for silk production. In Devon spiders finally left the underwater life and started to develop special organs for silk production because of a new terrestrial way of life. Former use of silk was rather simple but even some recent species haven't evolved their silk use to some more complex uses. Spider webs are told to be the most complex use of spider silk. The typical example on which I described the whole process of web creating is an orb web made by an orb weaver. Creation of web is genetically determined feature. Those ancient species have already been showing a base for development of spider behavior that we see in recent species. The proof that spider webs are not the final result of evolution are some spiders like Lycosidae, Pisauridae and Salticidae which primarily had the ability to produce webs but lost it due to its development of different ways of prey catching. Because of the expressed differentiation, which is the product of adaptive radiations since Paleozoic, spiders inhabit almost every type of environment and fulfill variety of ecological niches. In my opinion, it was primarily the use of spider silk that caused the evolutionary success of spiders, therefore I'd agree with the assertion of M. R. Gray from 1978 that the evolutionary development of spider silk has been of equal importance as the development of wings in insects and warm-bloodedness in vertebrates. Except the importance of that kind of evolution for spiders, I also see the greatest potential for its human use. Unfortunately, nowadays spiders and their silk are poorly examined but could be of great help in development of new ways of textile production that would be completely ecological and with no or very little impact on environment. It could also be of use in medicine, technology and other sciences which are of great importance for human population.