Voice over Internet Protocol (VoIP) is a method of transmitting audio and video over a network. It is a low-cost and readily available alternative to traditional landline phones. In this paper we discuss the foundational protocols of VoIP and analyze the Quality of Service (QoS) of several applications. Our testing consisted of capturing packets during a conversation to determine packet loss, throughput, delay, and jitter. Several listeners subsequently provided Mean Opinion Scores (MOS) of several audio snippets based on phonetic clarity. We determine that Skype provides the highest quality and most consistent service.