We discuss the impact of the charm quark mass in the CTEQ NNLO global analysis of parton distribution functions of the proton. The $bar{rm MS}$ mass $m_c(m_c)$ of the charm quark is extracted in the S-ACOT-$chi$ heavy-quark factorization scheme at ${cal O}(alpha_s^2)$ accuracy and found to be in agreement with the world-average value. Impact on $m_c(m_c)$ of combined HERA-1 data on semiinclusive charm production at HERA collider and contributing systematic uncertainties are reviewed.
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