A patent is a limited grant to an inventor by which he may exclude others from making, selling or using the invention. Government issue patents to inventors to encourage open publication of inventions and to expedite their widespread use. Although patents teach a technology and are therefore a type of technical publication, they also are an intellectual property having commercial value. This paper describes the variety of values a patent may have, both to the inventor himself and to a firm which acquires rights to it, and notes the special value of a patent in protecting investment in research, development, and realization of an invention as a product.