The cost of developing a medicine is huge: generally over $1.5 billion. In contrast, the cost of manufacturing the medicine is small, sometimes just a few dollars or even a few cents per unit dose. The profit margin on the sales price of the medicine thus needs to be high, in order to enable the drug originator to recoup the massive cost of developing the medicine. The sales price can only be maintained if the medicine is on the market with no direct competition. Once there is competition on price, the sales price of the medicine collapses. All of the costs of the development of the drug must be recouped before that price collapse, and patents are the main tool that a drug originator has to maintain its exclusivity. Patents are thus key to the viability of a drug development company as a business. It is vital that scientists working in drug discovery gain a good working knowledge of the patent system, both to avoid costly errors, and to help flag inventions when they are made. This chapter aims to give an insight into what patents are, what they can do, and how they are obtained and used.