Patent literature is an essential tool for anyone interested in engineering technology or competitive intelligence.  In the language of the U.S. statute, any person who "invents or discovers any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof, may obtain a patent therefor, subject to the conditions and requirements of this title. These classes of subject matter taken together include practically everything that is made by man and the processes for making the products. useful improvement thereof, may obtain a patent," subject to the conditions. 

The patent protects an idea and is often the most complete description of a technical discovery available to the public.  The patent gives the inventor the right to exclude others from making, using, or selling the invention in the U.S. for the full term of the patent, which is seventeen years for the ordinary patent and fourteen for the design patent.  And since patents contain complete descriptions you can research technical details and track business trends of your competitors.
What can be patented?  What are the terms of a U.S. patent?  Who may apply for a patent?  Patent research is now made easier through the internet.  Below are a few of the most valuable and useful internet patent resources, but this list barely scratches the surface.