Book excerpt: The Gleason system is the most important prognostic marker of prostate cancer that is critical to patient management and drives therapies across all disciplines dealing with prostate cancer. In addition to an extensive number of photographs, this book discusses in detail clinically related issues that are crucial for the urologist, radiotherapist, and oncologists to know, such as predicting upgrading and downgrading from needle biopsy to radical prostatectomy, risk of Gleason grading change over time, significance of tertiary grade patterns, and prognosis and implications related to various Gleason scores and different therapies. Images that were particularly difficult for contributing pathologists sent in for consultation are used in addition to classic examples, as these cases are the most informative in showing the difficulties with Gleason grading.