Each patent application must include a "specification" that "teaches one of ordinary skill in the art how to practice the claimed invention without undue experimentation, in the best mode known to the applicant on the filing date."

Simply stated, the Specification typically includes a textual Description portion, and frequently several drawing Figures, that together communicate how to make and how to use the claimed invention. This communication should be directed at someone who understands the basic concepts and jargon of the technology, but who is not necessarily an innovator or creative thinker. The application should explain the best manner for making and using the claimed invention, as of the date the application is filed.

Generally, each word used in the claims should appear in the Description. Each significant component of the claimed invention should be described thoroughly, both structurally and functionally.  Any known alternatives of those components should also be described.  Any special meaning attached to any term in a claim should be thoroughly defined or described.  Many claim terms can be described conveniently via examples.

Claims in the unpredictable technology areas, such as chemistry, biology, and some cutting-edge areas of physics, should be supported by experimental data that appears in the Description section and that evidences at least limited operability of the claimed invention. An explanation of the practical utility of such inventions should also be provided.

According to U.S. law, the Specification must also include a Title, a Brief Description of the Figures, and an Abstract.

Contrary to the traditional approach of many patent attorneys and agents, U.S. law does not require a Background or Summary section, comparisons to "prior art", or discussions of objects or advantages of the invention.  Moreover, opposing litigators have been known to use such language and/or statements made during prosecution, to destroy the resulting patent (i.e., convince a court to issue a judgment that the claims are not infringed or are invalid).