  We study the effect of the charm quark mass in the CTEQ global analysis of
parton distribution functions (PDFs) of the proton. Constraints on the
$\bar{\rm MS}$ mass of the charm quark are examined at the
next-to-next-to-leading order (NNLO) accuracy in the S-ACOT-$\chi$ heavy-quark
factorization scheme. The value of the charm quark mass from the hadronic
scattering data in the CT10 NNLO fit, including semiinclusive charm production
in DIS at HERA collider, is found to agree with the world average value.
Various approaches for constraining $m_{c}$ in the global analysis and impact
on LHC cross sections are reviewed.
