The language of adult foreign-language learners is rarely native-like, especially in their pronunciation, in which foreign-accented speech is the norm. Having a foreign accent, however, does not mean that a speaker will be unintelligible, nor that they cannot effectively communicate. Listeners are remarkably flexible in understanding varying pronunciation patterns. This chapter explores the relationship of intelligibility to pronunciation, especially with regard to foreign-accented speech. Intelligibility includes both actual understanding and the degree of effort involved in understanding (called comprehensibility). Research has demonstrated that pronunciation deviations are a major factor in loss of intelligibility. Despite opportunities for unintelligibility based on pronunciation differences, it may be surprising that foreign-accented speech is mostly intelligible, especially for listeners who are familiar with particular foreign accents. The ability of listeners to understand each other despite significant variations in pronunciation shows that people typically demonstrate a great deal of flexibility in communication. This flexibility is necessary for native accent differences, but more necessary for nonnative accents, in which pronunciation variations are more likely to be unexpected or outside the range of familiar native-speaker dialects. The chapter describe the types of pronunciation features that seem to be most important in intelligibility.