“Software timer manager” refers to a utility program typically implemented in a real-time system to allow tasks to install timers with granularities that are higher than the hardware timing resolution. A software timer manager may employ various data structures to keep track of user-installed timers. In this chapter, we focus on a structure called a timing wheel, and its extension called a hierarchical timing wheel. In particular, we explain the installation of timers with various timing requirements and the cause of precision errors. Pseudocode for implementing a hierarchical timing wheel is also provided.