This chapter describes the phonological system of English. This includes information about terms frequently used by speech and language therapists. Speech sounds are created through a complex system of movements in the vocal tract, which stretches from the lungs up through the larynx, mouth and nose. Some speech sounds are produced with vibration of the vocal folds or ‘voice’ such as the consonants ‘b’, ‘d’, ‘z’, ‘j’ and ‘m’ and some are voiceless such as ‘p’, ‘t’, ‘s’, ‘f’ and ‘ch’. The vowels are all voiced. The vocal folds produce the vibrations that make the main noise in speech. The larynx is also the source for one other sound that is common in English. The phonology of a language is the system of sounds in the language, and how the sounds combine. Phonemes are an abstract ‘idealised’ unit. One way to think about phonemes is analogous to the way letters are written in rapid handwriting.