  We report the first experimental results on spin-dependent elastic weakly
interacting massive particle (WIMP) nucleon scattering from the XENON1T dark
matter search experiment. The analysis uses the full ton year exposure of
XENON1T to constrain the spin-dependent proton-only and neutron-only cases. No
significant signal excess is observed, and a profile likelihood ratio analysis
is used to set exclusion limits on the WIMP-nucleon interactions. This includes
the most stringent constraint to date on the WIMP-neutron cross section, with a
minimum of $6.3\times10^{-42}$ cm$^2$ at 30 GeV/c${}^2$ and 90% confidence
level. The results are compared with those from collider searches and used to
exclude new parameter space in an isoscalar theory with an axial-vector
mediator.
