Exhibit 21

LIST OF SUBSIDIARIES

Stamps.com Inc.’s direct wholly owned subsidiaries are:

PhotoStamps Inc., a California corporation;

Auctane LLC, a Texas limited liability company, d/b/a ShipStation;

Interapptive Inc., a Missouri corporation, d/b/a ShipWorks;

PSI Systems, Inc., a California corporation d/b/a Endicia; and

ShippingEasy Group, Inc., a Delaware corporation.

In addition, ShippingEasy, Inc., a Delaware corporation, is wholly owned by ShippingEasy Group, Inc. and is an indirect wholly owned subsidiary of Stamps.com Inc.