While radiation dosimetry is no longer the ""hot topic"" of research that it once was, new treatment modalities still have challenges to be solved and detector systems are constantly being developed. But as a relatively mature subject, there is no widely-used current book devoted to clinical dosimetry. A primary purpose of this book is to help in the education of clinical physicists who have not had access to the forefront research into understanding radiation dosimetry. Making sure the dose delivered to the patient is what it should be is one of the most important jobs medical physicists have. There are many aspects to doing this, but at the core, the radiation must be accurately measured. One of the original major tasks of the AAPM was to establish methods which its members could use to reliably carry out this task, and it has been highly successful. There have been clinical dosimetry protocols and formalisms for brachytherapy dosimetry developed, calibration laboratories accredited, and a myriad of task group reports produced on different dosimetry techniques and delivery modalities.