At H-burning temperatures in the Sun, nuclear cross sections are extremely small and experimental measurements in a laboratory at the Earth's surface are hampered by the cosmic background. The LUNA collaboration has exploited the unique features of LNGS underground laboratory in terms of background reduction, to study very important H-burning reactions at astrophysically relevant energies. This paper will focus on the results recently obtained for the 3 He( 4 He,γ) 7 Be reaction using two

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... ent experimental techniques and with a close eye on the minimization of the systematical uncertainties. On going and future measurements will also be presented.