It might not be quite so direct, but there are a number of ad-network companies focused on exactly this. It can work like: 1) Sign-up for a "rewards card" or

It might not be quite so direct, but there are a number of ad-network companies focused on exactly this. It can work like: 1) Sign-up for a "rewards card" or mailing list at a store 2) Use a credit card with that account 3) That account is linked to that card within the network or sold to a network 4) The ad-network profile is then leveraged with a variety of e-commerce sites through cookies and the like 5) Purchases made online with those cookies are linked to purchase histories and profiles You can see how these network profiles are developed and interlinked until "spooky" things start happening. Following a consumer from brick and mortar stores to online is an advertising/e-commerce dream. I know several ad-networks are working towards developing graph databases linking profiles across devices.