Consonant clusters need to be produced and perceived accurately or intelligibility may be reduced. However, they are inadequately addressed even in traditional pronunciation materials. Because languages differ in the degree that they permit multiple consonants to occur as the onset or coda in a syllable, L2 learners may need to learn to produce and perceive different types of syllables when learning an L2. This may not only result in substitutions of sounds within the clusters, but also deletions of sounds or insertions of vowels to make words more pronounceable. This can, and often does, affect intelligibility because of the effects of mispronunciations on syllable structure. Because the exact nature of syllable structure is a matter of language-specific phonotactics, it creates the potential for unique types of intelligibility problems. The chapter argues that consonant clusters are important in word identification, and thus are important for intelligibility. But their pronunciation may be subject to cluster simplifications, either through deletion or epenthesis. Second, the chapter argues that final clusters may be affected by inflectional endings (especially –ed, –s, –’s), where simplifications may cause problems with intelligibility because of the loss of grammatical information.