MAX SCHREMS, a 24-year-old law student from Salzburg, Austria, wanted to know what Facebook knew: He requested his own Facebook file. What he got turned out to be a virtual bildungsroman, 1,222 pages long. It contained wall posts he had deleted, old messages that revealed a friend’s troubled state of mind, even information that he didn’t enter himself about his physical whereabouts.

Mr. Schrems was intrigued and somewhat rattled. He wasn’t worried about anything in particular. Rather, he felt a vague disquiet about what Facebook could do with all that information about him in the future. Why was it there at all, he wondered, when he had deleted it? “It’s like a camera hanging over your bed while you’re having sex. It just doesn’t feel good,” is how he finally put it. “We in Europe are oftentimes frightened of what might happen some day.”

Mr. Schrems’s sentiment is emblematic of the discomfort sweeping through Europe about the ways in which Internet companies treat personal information. That discomfort has, in turn, prompted proposals for stricter regulation of online data across the continent. And Europe’s moves to protect Internet privacy — something Americans have not, as yet, actively agitated for — have given rise to a thorny question: How do the laws and mores of different nations manage, if at all, the multinational companies that now govern our digital lives?

Personal data is the oil that greases the Internet. Each one of us sits on our own vast reserves. The data that we share every day — names, addresses, pictures, even our precise locations as measured by the geo-location sensor embedded in Internet-enabled smartphones — helps companies target advertising based not only on demographics but also on the personal opinions and desires we post online. Those advertising revenues, in turn, make hundreds of millions of dollars for companies like Facebook, which announced last week that it was going public in what is expected to be the largest I.P.O. in digital history. And those revenues help to keep the Web free of charge.