Abstract: This study shows that future abnormal returns to R&D increases are concentrated around subsequent earnings announcements. It further shows that market expectations, implied from stock prices, underestimate the future earnings benefits of increase in R&D. Finally, it documents that in their forecasts of future earnings, security analysts also underestimate the effect of increase in R&D spending. These results suggest that future abnormal returns following R&D increases are at least in part due to the market's underestimation of the earnings benefits of R&D increases. The finding in this study contributes to the longstanding debate in accounting on whether the US GAAP requirement to expense R&D costs when incurred causes investors to underestimate the benefits of R&D.