The design of a new neutrino detector, Borex, is illustrated in this paper. The main experimental features of this detector along with its principal physical goals are thoroughly discussed. The key features of the liquid scintillation spectroscopy detection technique adopted in the design of the detector are deeply explained. The main advantages of this technique, i.s. high energy resolution, low detection threshold, ability to distinguish between different neutrino detection modes, background discrimination, make Borex a powerful and flexible experimental tool able to test and measure the flux, the flavor content, the energy spectrum, the antineutrino content of the solar neutrino flux arriving at Earth. Borex is thus equipped to probe completely the particle physics of solar neutrinos. Due to its characteristics, this experiment, planned to be carried out at the Gran Sasso Laboratory, is expected to be a fundamental step towardsthe solution of the solar neutrino problem.