This thesis deals with Galactic cosmic-ray electrons and positrons (CRe). I present a stereo MAGIC data analysis optimized for diffuse sources of emission. New tools and Monte-Carlo (MC) particle production are essential ingredients of this method. I have applied a specific, non-conventional cleaning algorithm to ~40 h of MAGIC data to finally obtain the CRe spectrum. The latter turns out to be described by a power-law with spectral index Γ = 3.35 ± 0.23stat ± 0.15sys in the energy range ∼200 GeV - 1.4 TeV. This result is consistent with previous recent results from Fermi-LAT and HESS
