Abstract: Both marital status and computer usage on the job have been found to increase earnings by as much as two additional years of schooling. If correct, these findings suggest that factors other than long-term human capital are key determinants of earnings. This analysis uses several identification strategies and data sources to determine the causal effect of marital status and computer usage on wages. First, analyzing commonly used data sets such as the Current Population Survey and the National Longitudinal Survey of Youth, I find that there are large cross-sectional effects of marital status and computer usage on wages. However, identifying these effects using changes in marital status and including a fixed-effect with computer usage, it is found that these variables have only a small effect on wages. Second, I identify the causal effect of marital status and computer usage on wages using within-twin contrasts in these variables to control for the effect of non-genetic or family background factors on earnings differences. The results also indicate that marital status and computer usage are not important causal determinants of earnings, even after adjustments are made for measurement error and within-twin differences in ability.