General relativity's energy and positivity: a brief history

I give a brief review of the search for a proper definition of energy in General Relativity (GR), a far from trivial quest, which was only completed after four and a half decades. The equally (or perhaps more) difficult task of establishing its positivity-it was to take another 15 plus years-will then be summarized. Extension to cosmological GR is included. Mention is made of some recent offshoots. An invitation to submit a review to the Proceedings of the Royal Society prompts revisiting a subject of central importance both to GR and to my own past research-its energy definition and positivity. While there are no loose ends left, a summary may be of some use to students and non-experts. Exposure to introductory GR is useful. We will divide this survey into two unequal parts: first, the original GR without a cosmological constant, then extend it to the rather different two cases of ?not equal 0.