It’s actually both. The site determines what categories of ads can be displayed, and the viewer profile determines which in those categories will be actually shown.

How does this tracking really works? Is it really this sophisticated behemoth of AI research that makes it impossible to avoid? Why is it that I get targeted as an balding middle aged man with erectile dysfunction when I'm not?

The adtech places I've worked at relied on cookies. They usually have massive networks of major sites and track your browser activity as you browse different.

However, the servers were always crashing and I was always wondering when the customers would figure out that they were throwing money away.

See here for common tracking techniques. https://www.howtogeek.com/115483/htg-explains-learn-how-webs...

In terms of what ads to show you, AI not really necessary. Often it's just for stuff you've searched for on Google, amazon etc.

Age and gender seem to be two of the more significant variables in ad selection. Many women I know started getting ads for baby stuff once they turned 26 despite having never been interested in the topic.

Cause you visited sites that those people also visit.

Also cause a lot of adtech is not sophisticated.

>How does this tracking really works?

Cookies and/or pixels - edit If you've opted out of being cookied, then you may be "targeted as an balding middle aged man with erectile dysfunction."