This article introduces a new nonparametric test to detect jump arrival times and realized jump sizes in asset prices up to the intra-day level. We demonstrate that the likelihood of misclassification of jumps becomes negligible when we use high-frequency returns. Using our test, we examine jump dynamics and their distributions in the U.S. equity markets. The results show that individual stock jumps are associated with prescheduled earnings announcements and other company-specific news events. Additionally, S&P 500 Index jumps are associated with general market news announcements. This suggests different pricing models for individual equity options versus index options. (JEL G12, G22, G14) Financial markets sometimes generate significant discontinuities, so-called jumps, in financial variables. A number of recent empirical and theoretical studies proved the existence of jumps and their substantial impact on financial management, from portfolio and risk management to option and bond pricing and hedging (see Merton, 1976;Bakshi et al., 1997Bakshi et al., , 2000Bates, 1996;Liu et al., 2003;Naik and Lee, 1990;Duffie et al., 2000, andJohannes, 2004). Despite advances in asset pricing models and their inference techniques, the studies have found that jumps are empirically difficult to identify, because only discrete data are available from continuous-time models, in which most of the aforementioned applications were studied. Our goal in this article is first to propose a new jump detection technique to resolve such identification problems. Further, we show that our technique provides a model-free tool for characterizing jump dynamics in individual equity and S&P 500 Index returns, which allows us to investigate different model structures for their option pricing.