Precision luminosity measurement with proton-proton collisions at the CMS experiment in Run 2

Precision luminosity calibration is critical to determine fundamental parameters of the standard model and to constrain or to discover beyond-the-standard-model phenomena at LHC. The luminosity determination at the LHC interaction point 5 with the CMS detector, using proton-proton collisions at 13 TeV during Run 2 of the LHC (2015--2018), is reported. The absolute luminosity scale is obtained using beam-separation (``van der Meer'') scans. The dominant sources of systematic uncertainty are discussed. When applying the van der Meer calibration to the entire data-taking period, a substantial contribution to the total uncertainty in the integrated luminosity originates from the measurement of the detector linearity and stability. The reported integrated luminosity in 2015--2016 is among the most precise luminosity measurements at bunched-beam hadron colliders.