M. A. K. Halliday is widely regarded as the father of Systemic Functional Linguistics, as well as having contributed important work to fields such as sociolinguistics and language acquisition. This overview will enable readers to understand and appreciate the significance of Halliday's work. Written by Professor Jonathon J. Webster, the editor of the Collected Works of Halliday, this is the definitive clear, concise and accessible introduction to this immensely important linguist.