This is a highly preliminary draft version of a book that aims to provide an in-depth description and analysis of the tone system of Yongning Na, a Sino-Tibetan language spoken in Southwest China. Work on the present document started in 2012. The draft has been circulated among colleagues. It is gradually being improved. Publication in book form is likely to take place only after several more years. Issues of formatting have not yet been addressed at this stage: each chapter constitutes a separate entity with its own page numbering and list of references.