Google Patents covers the entire collection of granted patents and published patent applications from the United States Patent and Trademark Office (USPTO) and the European Patent Office (EPO). U.S. patent documents date back to 1790, while EPO patents go back to 1978. Google Patents uses the Cooperative Patent Classification (CPC).
A patent is the intellectual property right granted by the U.S. Government to an inventor "to exclude others from making, using, offering for sale, or selling the invention throughout the U.S. or importing the invention into the U.S." for a limited time in exchange for public disclosure of the invention when the patent is granted. In most cases, this is twenty years from the date of application. In some situations, the term of the patent may be extended due to delays in the processing of the application. After the patent has expired, the invention becomes public domain. In addition, patent owners must pay a maintenance fee at 3.5, 7.5, and 11.5 years after issue or else the patent will expire.
Utility patent: Describes a new and useful process, machine, article of manufacture, or composition of matter, or useful improvement thereof (i.e. what something does)
Design patent: A new, original, and ornamental design for an article of manufacture (i.e. how something looks)
Plant patent: Describes an asexually reproduced distinct and new variety of plant (e.g. ‘NuMex Heritage 6-4’ New Mexican Chile Pepper)
Whys & hows of patent searching
You have an idea for an invention — or have gone so far as to create a prototype. Before marketing your invention, you will need to determine if your invention has already been patented. To do this, conduct a thorough patent search. This will usually involve searching a number of different patent sites, so it's useful to keep a log of all your search activity to avoid duplicate efforts.