Incarcerated adults demonstrate substantially weaker numeracy and literacy skills compared to adults in the general population; nonetheless, little is known about the skills of incarcerated adults. Therefore, the purpose of this study was to examine individual and prison factors influencing the literacy and numeracy skills of offenders in the United States. The sample included 1,247 inmates from the Program of International Assessment of Adult Competencies. Path analysis results revealed educational attainment, native language, and book exposure were statistically significant predictors of skills. Although demographics were related to differences in performance, these effects appeared to be related to other variables. Finally, prison job training and engagement in numeracy activities were statistically significant predictors for numeracy. Findings from this study provide empirical evidence on how prison factors may influence the literacy and numeracy performance of inmates from diverse backgrounds. The findings also suggest a need for a closer evaluation of prison programs.