The Principal Register is reserved for marks that are inherently distinctive or that have acquired distinctiveness. For more information on the spectrum of trademark distinctiveness, please see our guide "What Factors Go Into Picking a "Good" Trademark?"
The Supplemental Register is available only to marks that are not inherently distinctive and have not acquired distinctiveness. Terms that are generic for the products or services applied for are unregistrable on either registry.
The Supplemental Register also has several other limitations. Applications requesting registration on the Supplemental Register or requesting amendment to the Supplemental Register must claim current use of the mark in the US, or be based on a pending foreign application or foreign registration under Section 44 of the Lanham Act. Intent-to-use applications and Madrid Protocol-based applications are not allowed on the Supplemental Register, even as pending applications. For more on Section 44 claims, please read our guide "What Is the Paris Convention?" and for more on Madrid Protocol filings, please read our guide "What Is the Madrid Protocol?"
Registration on the Supplemental Register has considerably less value than registration on the Principal Register: it provides notice to third parties of the registrant’s claim of rights in the mark, and will help prevent third-party registrations for very similar marks for closely related goods. For more on the additional benefits of registration on the Principal Register, please read our guide on the benefits of registration.