What is the role of cookies in e-commerce?

Cookies are small text files stored in the browser's directory or in the user's data folder. They are information that helps identify the user on the site. In e-commerce they let us identify users and serve them marketing messages, or store data about products added to the cart: when the customer returns, the products from the previous visit will still be there. Cookies also play a role in ads served across the web — by identifying recipients, advertised content is matched to their internet activity history.