Book excerpt: This book provides a wealth of images and extensive information on circulating tumor cells (CTCs) and other cells usually observed in blood from patients with cancer, such as giant macrophages, and circulating tumor microemboli (CTM). The field of “liquid biopsy” began with the analysis of CTCs in the early 2000s. In the beginning, molecular techniques were developed to detect these cells in the blood. However, it has since become clear that CTCs initially require a cytopathological analysis to be detected without false positive and negative results. After detection, molecular analysis can be subsequently performed. Cancer is an important cause of mortality, especially when detected in late stages. Even with all the advances that have been made in its treatment, cancer is still challenging, as many patients do not respond to any therapy. Many health agencies have considered early diagnosis as a feasible tool. In this context, it is of the utmost importance to know the morphology and characteristics of CTCs to determine a correct diagnosis. Currently much of the scientific community is committed to expanding our knowledge of CTCs, and this work makes a valuable contribution, presenting hundreds of cell images from patients with various types of cancer, in many different stages of disease, and after receiving various treatments. The Atlas of Liquid Biopsy: Circulating Tumor Cells and Other Rare Cells in Cancer Patients’ Blood is an essential reference guide for all physicians, biologists, biomedics, and professionals working at clinical and research laboratories, hospitals and research centers.