  We prove trace theorems for weighted mixed norm Sobolev spaces in the
upper-half space where the weight is a power function of the vertical variable.
The results show the differentiability order of the trace functions depends
only on the power in the weight function and the integrability power for the
integration with respect to the vertical variable but not on the integrability
powers for the integration with respect to the horizontal ones. They are new
even in the un-weighted case and they recover classical results in the case of
un-mixed norm spaces. The work is motivated by the study of regularity theory
for solutions of elliptic and parabolic equations with anisotropic features and
with non-homogeneous boundary conditions. The results provide an essential
ingredient to the study of fractional elliptic and parabolic equations in
divergence form with measurable coefficients.
