After having quickly reviewed the basic concepts upon which Montecarlo
event generators are built, I will explain how NLO QCD corrections can
be included in these tools, focusing mostly on the powheg method. I will
then show how a more recent idea (MiNLO) has allowed to generate events
with simultaneous NLO accuracy in different jet multiplicities, and how
it can be applied to get NNLO accurate predictions matched to parton
showers.