IDX stands for "Internet Data Exchange", commonly called Broker Reciprocity. Broker Reciprocity is the primary means of enhancing cooperation between REALTORS® to facilitate the purchase and sale of real property. IDX/Broker Reciprocity provides MLS participants the tool they need to download and display each others' listing information on their Internet Web sites. Under Broker Reciprocity, brokers exchange consent to display each others listings and have full control over which listings they display.