Ads sold by Amazon, once a limited offering at the company, can now be considered a third major pillar of its business, along with e-commerce and cloud computing. Amazon’s advertising business is worth about $125 billion, more than Nike or IBM, Morgan Stanley estimates. At its core are ads placed on Amazon.com by makers of toilet paper or soap that want to appear near product search results on the site.

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In addition to knowing what people buy, Amazon also knows where people live, because they provide delivery addresses, and which credit cards they use. It knows how old their children are from their baby registries, and who has a cold, right now, from cough syrup ordered for two-hour delivery. And the company has been expanding a self-service option for ad agencies and brands to take advantage of its data on shoppers.

Karen Weise on Amazon’s next product.

(Hint: the Product is You.)