  Muons and neutrinos from cosmic ray interactions in the atmosphere originate
from decays of mesons in air-showers. Sibyll-2.3c aims to give a precise
description of hadronic interactions in the relevant phase space for
conventional and prompt leptons in light of new accelerator data, including
that from the LHC. Sibyll is designed primarily as an event generator for use
in simulation of extensive air showers. Because it has been tuned for forward
physics as well as the central region, it can also be used to calculate
inclusive fluxes. The purpose of this paper is to describe the use of
Sibyll-2.3c for calculation of fluxes of atmospheric leptons.
