We present equations of state relating the phases and a three-dimensional phase diagram for ammonia with its solid, liquid, and vapor phases, based on fitted authentic experimental data and including recent information on the high-pressure solid phases. This presentation follows similar articles on carbon dioxide and water published in this "Journal", where the basics of multiple-phase equilibria are described. Such an authentic diagram for ammonia has not been presented and may improve the understanding of its phase relationships. Interactive virtual 3D versions of these phase diagrams, programmed in Jmol, are also available. Since the phase data on ammonia has not been comprehensively collated in recent years, a chronological bibliography of relevant publications is included. (Contains 2 figures.)