Fusion power is one of a very few sustainable options to replace fossil fuels as the world's primary energy source. Although the conditions for fusion have been reached, much remains to be done to turn scientific success into commercial electrical power. Fusion has progressed from the insight of Sir Arthur Stanley Eddington in 1920 and Fermi's speculations in 1946 to the threshold of fusion burn at JET at Culham and soon in the international experiment ITER. The challenge of providing carbon free energy for the whole world is greater than ever. We need fusion. In this Sydney Ideas lecture, Professor Steven Cowley, theoretical physicist and international authority on nuclear fusion and astrophysical plasmas, and President of Corpus Christi College Oxford examines two key questions: What scientific questions must be resolved and how can we hasten the first fusion electricity?