  The MAJORANA DEMONSTRATOR is searching for neutrinoless double-beta decay in
$^{76}$Ge with two modular arrays of natural and $^{76}$Ge-enriched germanium
detectors. It is located at the 4850 level of Sanford Underground Research
Facility in Lead, South Dakota, USA, and its total mass of germanium detectors
is 44.1 kg, of which 29.7 kg is enriched. The analysis of the first 26 kg-yr of
data provides an unprecedented energy resolution of 0.13% in the region of
interest at 2039 keV and a background level of 15.4 $\pm$ 2.0 counts/(FWHM t
yr). It establishes the lower limit of the half-life of neutrinoless double
beta decay as 2.7 10$^{25}$ yr in 76Ge at 90% CL. This analysis will be
summarized here with an emphasis on the energy determination.
