CERN-LHC. Four-lepton production in proton-proton collisions, pp to (Z/gamma*)(Z/gamma*) to l+l-l'+l'-, where l, l' = e or mu, is studied at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 2.6 inverse femtobarns. The ZZ production cross section, sigma(pp to ZZ) = 14.6 +1.9/-1.8 (stat) +0.5/-0.3 (syst) +/- 0.2 (theo) +/- 0.4 (lumi) pb, is measured for events with two opposite-sign, same-flavor lepton pairs produced in the mass region 60 < m[l+l-], m[l'+l'-] < 120 GeV. The Z boson branching fraction to four leptons is measured to be B(Z to l+l-l'+l'-) = 4.9 +0.8/-0.7 (stat) +0.3/-0.2 (syst) +0.2/-0.1 (theo) +/- 0.1 (lumi) x E-6 for the four-lepton invariant mass in the range 80 < m[l+l-l'+l'-] < 100 GeV and dilepton mass m[l+l-] > 4 GeV for all opposite-sign, same-flavor lepton pairs. The phase spaces for all fiducial cross section measurements include the following requirements: - 4e, 4mu, or 2e2mu (opposite-sign, same-flavor pairs) - All opposite-sign same-flavor lepton pairs m[l+l-] > 4 GeV - All leptons |eta| < 2.5 - Leading lepton pt > 20 GeV - Second lepton pt > 10 GeV - All lepton pt > 5 GeV The ZZ to lll'l' fiducial cross section phase space further requires the following: - Both dileptons in 60 < m[l+l-] < 120 GeV The Z to lll'l' fiducial cross section and branching ratio measurements further require the following: - mZ1 > 40 GeV where Z1 is the lepton pair with invariant mass closest to the nominal Z mass - 80 < m[l+l-l'+l'-] < 100 GeV The phase space for the total ZZ cross section measurement is defined as: - Both Z bosons are required to have invariant mass between 60 and 120 GeV.