  We report on the first cross section measurement of charged-current single
charged pion production by neutrinos and antineutrinos on argon. This analysis
was performed using the ArgoNeuT detector exposed to the NuMI beam at Fermilab.
The measurements are presented as functions of muon momentum, muon angle, pion
angle, and angle between muon and pion. The flux-averaged cross sections are
measured to be $2.7\pm0.5(stat)\pm0.5(syst) \times 10^{-37}
\textrm{cm}^{2}/\textrm{Ar}$ for neutrinos at a mean energy of 9.6 GeV and
$8.4\pm0.9(stat)^{+1.0}_{-0.8}(syst) \times 10^{-38}
\textrm{cm}^{2}/\textrm{Ar}$ for antineutrinos at a mean energy of 3.6 GeV with
the charged pion momentum above 100 MeV/$c$. The results are compared with
several model predictions.
