The Borexino experiment has begun data taking in May 2007 after a long R&D work and preparation. The liquid scintillator purity exceeds even optimistic expectations, and the first detection of 7Be solar neutrinos has been possible after less than two months of data taking. This note shows briefly which are the main issues that were addressed in order to obtain such an extreme radiopurity, the detector performance and a few details concerning this first result.