A cookie is a small piece of information that the browser writes on the device (computer, mobile, tablet, smart screen, etc) of the user. There are first party cookies or third party cookies. First party cookies are the ones that belong directly to the website you are browsing. If you visit, all the cookies hosted in are first party cookies. If you have a paypal cookie on, this cookie will be considered a third party cookie, as it´s outside the domain. Same happen with all the cookies that collect audiences, like doubleclick, adform, google or facebook, for example.

Cookies are very important for online advertising as they are one of the keys for all the system. With the cookies, all the ad tech companies, like facebook and google, can identify the websites that one specific user see and match with other data sources, like your logins. This information can be used then, by advertisers, to target users.

Cookies allow advertisers to cap the number of impressions / exposures per user and measure all the interactions per user. Cookies are then what allow advertisers to be more intelligent when they advertise in a programmatic way.

Alternatives to Cookies: with the mobile devices, many ad tech companies are trying to find ways to avoid the use of cookies, as it´s the technology is not 100% accurate, especially in the app environment, where cookies are not used. On Mobile devices, and in the new desktop Operative Systems there is available the advertising id. This Id then allows all the ad tech companies to identify the devices by the id instead of using the cookies. What most of ad tech companies are doing is match the different sources of information (browser, logins, advertising id´s, network, ip address, device name, cookies) into one database. So the audiences and tracking are more and more accurate.