The North American Industry Classification System (NAICS) are industry codes that define establishments based on the activities in which they are primarily engaged. NAICS codes are also used for administrative, contracting, and tax purposes.
SBA uses NAICS as a basis for its size standards. Size standards using NAICS as their basis apply to all Federal government programs, including procurement. When the Federal government intends to acquire goods or services, it identifies the NAICS code that describes the principal purpose of that procurement.
Your business may have myriad capabilities, and the NAICS code for a given procurement opportunity may not be the same as your primary NAICS code. That will not keep you from bidding or making an offer, so long as you meet the size standard for the procurement and have the capacity to provide the goods or services.
Visit the United States Census Bureau NAICS website to identify your NAICS code(s).