This first part of the 2-part MDS and MPN lecture series includes an introduction to general principles of diagnosing myeloid neoplasms and the tools needed to effectively diagnose and classify MDS and MPN entities. The diagnosis of myeloproliferative neoplasm (MPN) entities is covered, including morphologic, clinical, and genetic criteria. Diseases covered are chronic myeloid leukemia, chronic neutrophilic leukemia, the JAK2-associated myeloproliferative neoplasms, and eosinophilic neoplasms (including the eosinophilias associated with specific genetic aberrations). This lecture is intended for residents during their hematopathology rotation as well as senior residents and hematopathology fellows wishing to review the principles of MPN diagnosis and classification.