How did the table fork acquire a fourth tine? What advantage does the Phillips-head screw have over its single-grooved predecessor? Why does the paper clip look the way it does? What makes Scotch tape Scotch? In this delightful book Henry Petroski takes a microscopic look at artifacts that most of us count on but rarely contemplate including such icons of the everyday as pins Post-its and fast-food clamshell containers. At the same time he offers a convincing new theory of technological innovation as a response to the perceived failures of existing products--suggesting that irritation and not necessity is the mother of invention.