  We investigate the potential of the International Linear Collider (ILC) to
probe the mechanisms of neutrino mass generation and leptogenesis within the
minimal seesaw model. Our results can also be used as an estimate for the
potential of a Compact Linear Collider (CLIC). We find that heavy sterile
neutrinos that simultaneously explain both, the observed light neutrino
oscillations and the baryon asymmetry of the universe, can be found in
displaced vertex searches at ILC. We further study the precision at which the
flavour-dependent active-sterile mixing angles can be measured. The measurement
of the ratios of these mixing angles, and potentially also of the heavy
neutrino mass splitting, can test whether minimal type I seesaw models are the
origin of the light neutrino masses, and it can be a first step towards probing
leptogenesis as the mechanism of baryogenesis. Our results show that the ILC
can be used as a discovery machine for New Physics in feebly coupled sectors
that can address fundamental questions in particle physics and cosmology.
