Addiction to psychostimulants such as methamphetamine (MA) is a significant public health issue in the United States with no FDA-approved pharmacological interventions. MA addiction is a heritable neuropsychiatric disorder, however, its genetic basis is almost entirely unknown. Available human genome-wide association studies (GWAS) lack sufficient power to detect the influence of common genetic variation on the risk of addiction. Mammalian model organisms offer an attractive alternative to more rapidly uncover novel genetic factors that contribute to addiction-relevant neurobehavioral traits. Using quantitative trait locus (QTL) mapping in mice, we identified a locus on chromosome 11 that contributed to a decrease in sensitivity to the locomotor stimulant properties of MA. To fine map this QTL, we generated interval-specific congenic lines and deduced a 206 kb critical interval on chromosome 11 that contained only two protein coding genes (Rufy1 and Hnrnph1). Replicate mouse lines heterozygous for Transcription Activator-like Effector Nucleases (TALENs)-induced frameshift deletions in Hnrnph1 (Hnrnph1+/-), but not in Rufy1 (Rufy1+/-), recapitulated the decrease in MA sensitivity observed in congenic mice; thus, identifying Hnrnph1 as a novel quantitative trait gene for MA sensitivity. Hnrnph1, an RNA-binding protein, has not previously been identified in human GWAS of neuropsychiatric disorders but has been implicated in mu-opioid receptor splicing associated with heroin dependence. The primary objectives of this dissertation is to (1) detail the forward genetic and reverse genetic approaches taken to identify Hnrnph1 as a quantitative trait gene for MA sensitivity; (2) assess the MA addiction-relevant behaviors presented by Hnrnph1+/- mice through conditioned place preference (CPP) and oral self-administration procedures; and (3) identify the neurobiological mechanisms through which Hnrnph1 affects behavior via transcriptome, immunohistochemical and neurochemical assessments of the mesocorticolimbic dopamine circuit. Overall, Hnrnph1+/- mice display increased dopaminergic innervation and MA dose-dependent dopamine release in nucleus accumbens, which could underlie reduced drug sensitivity, reward, and reinforcement. The results of this thesis provide substantial evidence to implicate Hnrnph1 in MA addiction.