books.google.co.inhttp://books.google.co.in/books/about/Language_as_a_Social_Semiotic.html?id=KSkLAQAAMAAJ&utm_source=gb-gplus-shareLanguage as a Social Semiotic
This is essential reading for anyone who wants to understand Halliday's thinking. It's a book I go back to time and time again and each time I get a something more from it.