Genomic resources developed for the domestic dog have provided powerful tools for studying canine evolutionary history and dog origins. Although X chromosome data are often excluded from these analyses due to their unique inheritance, comparisons of the X chromosome and the autosomes can illuminate differences in the histories of males and females as well as shed light on the forces of natural selection. Here we use X chromosome single nucleotide polymorphisms (SNPs) to analyze evolutionary relationships among populations of gray wolves worldwide in comparison to domestic dogs, and investigate evidence of selection. The results are concordant with population structure indicated by autosomal data. We additionally conducted a selection scan to identify loci that are putatively under selection.