Recent studies have explored how pronunciation teachers' knowledge, beliefs, and opinions about teaching influence their classroom practices. In addition, recent research has demonstrated the eff effectiveness of nonnative-speaking (NNS) teachers in pronunciation instruction. However, very little is known about the knowledge base that allows NNS teachers to implement pronunciation instruction. This is an area that requires further inquiry because of the central role of pronunciation in oral communication, the number of NNS teachers of English worldwide, and because of the communication needs among speakers of different varieties of English. This case study investigated the knowledge base of an experienced in-service NNS pronunciation teacher in an English-as-a-foreign-language context. Using qualitative data-gathering methods (e.g., classroom observation, semistructured interviews, and stimulated-recall interviews), and Shulman's "Knowledge Base Framework," the study demonstrates that the knowledge base that allows an NNS teacher to implement pronunciation teaching is composed of categories of knowledge interrelated in complex ways. Building upon these findings, the study also uncovers how factors such as previous learning and teaching experiences shape the beliefs and pedagogical actions of such teacher in implementing pronunciation instruction.