This document presents an empirical study of dormant bugs. The study analyzed over 20 open-source systems to understand dormant bugs. The key findings are: 1) Approximately 29% of bugs are dormant bugs that remain undetected for long periods. 2) Dormant bugs are fixed faster (median of 5 days) and with larger fixes (median of 19 lines of code) than non-dormant bugs. 3) Developers who fix dormant bugs tend to be more experienced than those who fix non-dormant bugs.