https://www.uspto.gov/patents/search/classification-standards-and-development
Patents technology is classified and indexed for searching by patent examiners using various methodology. On this page, learn about the classification system...
patent classificationuspto
https://www.uspto.gov/about-us/events/cooperative-patent-classification-combination-sets
This Classification Cafe session will provide Cooperative Patent Classification (CPC) information for Combination Sets (C-Sets).
patent classificationcooperativecombinationsetsuspto