Occupation refers to the type of job an individual holds. Industry refers to the type of business. The two don't necessarily coincide. For example, a computer programmer may work for an advertising agency, and an advertising sales agent may work for a software company.

Occupations are usually classified by Standard Occupational Classification (SOC) categories (developed by the Department of Labor). Each occupation is assigned a 6-digit code. The first two digits represent a broad occupational classification, and additional digits represent more detailed sub-divisions. For example

• 11 = Management Occupations
• 11-10 = Top Executives
• 11-1030 = Legislators

Historically, the US government classified businesses using Standard Industrial Classification (SIC) codes. However, beginning with 1997 most data products switched to the North American Industry Classification System (NAICS). Concordance tables are available for conversion between the two systems. Both SIC and NAICS codes are hierarchical in nature. The first two digits represent a broad industry category, and each digit afterwards represents a sub-division. For example, in NAICS

• 44 = Retail Trade
• 445 = Food and Beverage Stores
• 4452 = Specialty Food Stores
• 44523 = Fruit and Vegetable Markets

The US Census Bureau uses its own sets of codes for both occupations and industries, but mappings are provided between these and the regular standards.