The single-server queueing system is very fundamental. A complex system such as the Internet can be decomposed into a set of interacting single-server queueing systems. This chapter shows in detail how to simulate the single-server queueing system. Packets are transferred to the server in the same order in which they enter the buffer. This buffering mechanism is referred to as the First-In First-Out (FIFO) mechanism. The response time is the total time a customer spends in the system. That includes waiting time and service time. Server utilization is the proportion of simulation time during which the server is busy. It is the product of its throughput and the average service time per customer. In the transient phase, output variables fluctuate due to the effect of the initial state of the simulation model. Thus, no simulation data should be collected during this phase.