This first volume in a series presenting the collected works of Professor M.A.K. Halliday contains seventeen papers, including a new piece titled A Personal Perspective in which Professor Halliday offers his own perspective on language and linguistic theory as covered in his collected works. The first part presents early papers (1957-1966) on basic concepts such as category, structure, class, and rank. The second part highlights how over the span of two decades (mid-sixties to mid-eighties) Halliday developed systemic theory to account for linguistic phenomena extending upward through the ranks from word to clause to text. The third part includes more recent work in which Halliday discusses the issues confronting those who would study linguistics, or as Firth described it language turned back on itself.