Google Patents - potentially easy and quick way to search for U.S. patents and patent applications by inventor, number, or keywords - it does not contains foreign patents (see  MicroPatent). Older patents will have spelling errors from optical character recognition.

MicroPatent - MicroPatent provides a database for searching and displaying the full text /images in PDF of US (1964+), US applications (2001+), EP (European Patents, 1980+), EP-A (European Patent Applications 1978+), and PCT (World Patents, 1978+). Searching and displaying full-text (no drawings) is available for US (1836-1963), Great Britain (1979+), and DE (German, 1989+) patent records as well as the front page of JP (Japanese, 1976+) documents. Older patents will have spelling errors from optical character recognition.Restricted to current Cornell users. See Guide to Using MicroPatent.

Patent Fetcher - if you know the patent number, searching free Patent Fetcher will download the PDF and print out all pages at once. It can be slow if the patent has many pages, and you are limited to 5 patents per 24 hours per ip address.

WikiPatents - WikiPatents has the largest database of patents open for public comment on the internet, allows PDF downloading of patents, free patent translation into multiple languages, and additional information and resources. 

FreePatentsOnline.com - requires registration to access PDFs of patents. Allows for RSS feeds and XML data downloads.

PatentStorm - U.S. patents from 1990 foward. Contains U.S. and foreign citing patents.

U.S. Patent and Trademark Office -  Official USPTO site. For 1976 to present you may search by patent class numbers as well as by keyword, inventor names. For 1790-1976 patents are retrieved only by patent number or U.S. class/subclass number. Includes full text and/or page images. Images require Tiff viewer. If you don't have the viewer, you can retrieve PDFs by patent number in Patent Fetcher, or search in MicroPatent, see next entry.

European Patent Office - view patents in their original language, or English abstracts and titles. from 1978 to date. Includes European (EP), World (WO), and Japanese (PAJ) patents.  Full text in Adobe Acrobat. Response time may be slow.

Interlibrary Loan - If the patent you need is not available from one of the above options, ask the Reference Desk to get a photocopy through interlibrary loan (no charge, takes 1-2 weeks). Foreign patents may also be requested.

Derwent Scientific and Patent Information - If you can't wait for interlibrary loan or the web, rush requests for the complete patent may be obtained from: Derwent - phone: 1-800-336-5010, fee varies.