Patent "classes" are categories for technologies with shared characteristics. Searching by classification is more reliable than searching by keywords, which can miss relevant patents described with different language.
If necessary, verify the definition and scope of a (sub)class by looking it up on the USPTO website, selecting Definitions.
Google Patents and the USPTO's databases have different advantages. Use both to ensure a comprehensive search strategy.
|All USPTO patent grants and published applications, except recent months||All USPTO patent grants and published applications, updated weekly|
|Single database for grants and applications||Separate databases for grants and applications|
|USPTO, EPO and WIPO patents||USPTO patents only|
|Easy-to-use Google-style interface||Complex interface for precise searching|
|Document searching for all patents||Document searching 1976-present, index searching 1790-1975|
|Searches images with Optical Character Recognition||Searches text (more reliable)|
|Displays documents as HTML and PDF||Displays documents as PDF (may require reader installation)|