Short codes, or short numbers, are short digit sequences, significantly shorter than telephone numbers, that are used to address messages in the Multimedia Messaging System (MMS) and short message service (SMS) systems of mobile network operators. In addition to messaging, they may be used in abbreviated dialing.

Short codes are designed to be easier to read and remember than telephone numbers. Short codes are unique to each operator at the technological level. Even so, providers generally have agreements to avoid overlaps. In some countries, such as the United States, some classes of numbers are inter-operator (used by multiple providers or carriers, U.S. inter-operator numbers are called common short codes).

Short codes are widely used for value-added services such as charity donations, mobile services, ordering ringtones, and television program voting. Messages sent to a short code can be billed at a higher rate than a standard SMS and may even subscribe a customer to a recurring monthly service that will be added to the customer's mobile phone bill until the user texts, for example, the word "STOP" to terminate the service.