The World Health Organization (WHO) has initiated a new project titled *World Health Organization Classification of Tumors*, which builds upon the *International Histological Classification of Tumors* and aims to standardize tumor classification. This new series will include histopathologic criteria and molecular genetics information, crucial for understanding cancer types and predicting treatment outcomes. The first volume, *Pathology and Genetics of Tumours of the Nervous System*, was published in 2000 and resulted from a collaborative effort by 106 neuropathologists and geneticists from 21 countries. The second volume, covering tumors of the digestive system, is currently in preparation. The project emphasizes rapid publication to keep up with advancements in tumor genetics and aims to cover all tumor sites within five years, making the WHO “Blue Books” a global standard reference.The World Health Organization (WHO) has initiated a new project titled *World Health Organization Classification of Tumors*, which builds upon the *International Histological Classification of Tumors* and aims to standardize tumor classification. This new series will include histopathologic criteria and molecular genetics information, crucial for understanding cancer types and predicting treatment outcomes. The first volume, *Pathology and Genetics of Tumours of the Nervous System*, was published in 2000 and resulted from a collaborative effort by 106 neuropathologists and geneticists from 21 countries. The second volume, covering tumors of the digestive system, is currently in preparation. The project emphasizes rapid publication to keep up with advancements in tumor genetics and aims to cover all tumor sites within five years, making the WHO “Blue Books” a global standard reference.