Abstract: A referral-tracking system accepts listings from originators and generates referral identifiers that represent referrals of those listings. A referral identifier represents a referral by the originator or by someone who, after receiving a listing identifier from an originator or someone else, applies to the system to be recognized as a referrer and has accordingly been issued a referral identifier that associates that requester with a listing to be referred. An originator or other requester applying for a referral identifier is given the option of identifying intended recipients to tracking system or not. If the requester does supply the tracking system with that information, the issued referral identifier is associated not only with the listings and the referring requester but also with the recipient. In that way, the system can provide conversion-rate information without discouraging participation by potential requesters who prefer not to divulge the recipients' identities.