In this report we describe the unique capabilities of the $\alpha /\beta$ discrimination of the Borexino experiment. This capability is the direct result of years of development aimed at the design of an experiment that could withstand contamination from $\alpha$-emitting nuclides. The combination of the excellent $\alpha /\beta$ discrimination and of the excellent radiopurity of the detector permitted to extract information on the solar neutrino interactions in Borexino without interference from $\alpha$ particles.