Between 2000 and 2019, the number of inmates in Australian prisons grew from 21,714 in 2000 to 43,028 in 2019, an increase of 98%, or in per capita terms, 48%. Much of this increase occurred between 2012 and 2019. In New South Wales (NSW), for example, the prison population rose by 17% in the 11 years between 2000 and 2011, but then grew a further 39% in the eight years between 2012 and 2019. A similar acceleration in inmate numbers occurred in other States and Territories after 2011. In this article, we examine the contribution of sentencing, bail, policing policy and crime to the rapid rise in NSW imprisonment rates. We cite evidence showing that the likelihood of bail refusal has changed very little over the period when imprisonment rates rose, we find no evidence of a significant change in the length of sentences and no evidence of an increase in the likelihood of a prison sentence once changes in sentence-relevant factors are taken into account. Most of the increase in imprisonment rates appears to be due to changes in policing policy and (to a lesser extent) certain types of crime.