This introduction presents an overview of key concepts covered in the subsequent chapters of this book. The book focuses on identifying changes in penal culture over the last 40 years, which have led to a re-valorisation of imprisonment as a frontline criminal justice strategy. The concept of penal culture is the explanatory principle around which the book is organised. The change from public to private was an uneven process mediated by understandings of race and gender. The exploration of penal culture in the book is the outcome of a larger study centred on the Australian Prison Project which was initially funded by the Australian Research Council. Similarly the warehousing of large number of people with mental health issues apparently is a defensible byproduct of the need for greater security and reduction in risk. Finally, It concerns the way a risk paradigm has transformed criminal justice and its specific impact on the use of imprisonment.