Sometimes here on Academia I read messages referring to American National Science Foundation (NSF), "the USA agency that supports fundamental research and education in all the non-medical fields of science and engineering" (page on Wikipedia).

In this question and this question we discussed about NSF postdoctoral funding possibilities. Since I am in the European Union, I don't know very much about NSF.

• How does NSF funding system work?
• How does NSF postdoctoral funding program work? Does it fund only American citizens or anyone that wants to work as a researcher in the US?

Many thanks!