The Patentability of Non-physical Investions: Lessons from the United States McEnieryBen 2019 Patent systems around the world are being pressed to protect new and exciting subject matter in order to keep pace with the rapid technological advancement of our age. This rapid development and pressure to expand the bounds of what has traditionally been recognised as patentable subject matter has created uncertainty regarding what it is that the patent system is actually supposed to protect. Among other things, the patent system has had to contend with uncertainty surrounding claims to horticultural and agricultural methods, artifi cial living micro-organisms, methods of treating the human body, computer software and business methods. The contentious issue of the moment is one at whose heart lies the important distinction between what is a mere abstract idea and what is properly an invention deserving of the monopoly protection afforded by a patent. That question is whether purely non-physical inventions, being methods that do not involve a physical effect or cause a physical transformation of matter, constitute patentable subject matter. This paper goes some way to addressing these uncertainties by considering how the Australian approach to the question can be informed by developments arising in the United States and canvassing some of the possible lessons we in Australia might learn from the approaches taken thus far in the United States.