Now that the full text of patents as well as patent searching tools are available for free on the Internet, every librarian who is responsible for assisting people with science and technology information should have a basic knowledge of this aspect of intellectual property. Whether a school librarian helping children discover the world of inventions, an academic librarian assisting an engineering major on a design assignment, the public librarian demonstrating how an independent inventor may do a patentability search, or a special librarian performing a patent search for the company's legal unit, patents are an integral part of the STM literature. At minimum, library staff should be able to recognize a patent citation and, depending on availability, to find the full text in one of the free patent databases on the web. Ideally, staff should be as comfortable with patents as they are with other science and engineering topics; they should know what resources to consult, and how to use those resources. This article is an introduction to patent reference for librarians who work in U.S. libraries and will give a foundation on which to build knowledge and skills in this area. Librarians who only occasionally receive patent questions may use this as a "how-to guide" with a list of resources. Although international patents are discussed, the guide is primarily U.S.-based, and covers what a patent is, provides basic searching techniques in the major free patent databases on the web, and links to patent information sources.