Merchants will usually fall into one of the four merchant levels based on credit card transaction volume over a 12-month period. Transaction volume is usually based on the aggregate number of transactions (inclusive of credit, debit and prepaid) from a merchant Doing Business As ("DBA").  In cases where a merchant corporation has more than one DBA, acquirers must consider the aggregate volume of transactions stored, processed or transmitted by the corporate entity to determine the validation level.

The various card-specific merchant level descriptions and requirements can be found at the following:

VISA Merchants
MasterCard Merchants
Discover Merchants
American Express Merchants
JCB-Global Merchants