Posttraumatic stress disorder (PTSD) can be a debilitating condition that affects 1 in 20 people. This lecture reviews our current knowledge of how PTSD develops, the course of PTSD, and the best available treatments. Apart from understanding the biological mechanisms of PTSD, social factors also play a critical role in adaptation to trauma. Recent examples of longitudinal analyses of survivors of Australian disasters will be described, including application of social network analyses following the Black Saturday fires. Many people do not respond to our best treatments and this review will address recent evidence of neural factors that identify treatment response and attempts to augment treatment by capitalizing on key neural mechanisms. Finally, the lecture will discuss PTSD at a global level, and review recent attempts to address PTSD in the millions of people affected by trauma in low and middle income countries that lack health systems.