body: I'm attempting to do some preliminary research on trademarks and having trouble with the US classification codes. E.g., I'm looking at a 'Goods and Services' description that starts with "IC 042. US 100 101."
  
  
  The IC designation is clear enough and it's easy enough to find [IC definitions](https://www.uspto.gov/trademark/trademark-updates-and-announcements/nice-agreement-current-edition-version-general-remarks).
  
  
  However, I can't find the US class definitions. I understand the IC system is the primary classification used for trademarks, however all (?) the trademark applications I see include 'US' code numbers as well, following the IC numbers and the [Trademark Manual of Examining Procedure](https://tmep.uspto.gov/RDMS/TMEP/current) refers to the US codes as "secondary".
  
  
  So, it seems the US codes are still useful—though secondary—but not defined anywhere I can find. Or should I just not worry about the US codes?
  
  
  
title: Where are the "United States Classification" codes for trademarks defined?