Recently, a point mutation in the JAK2 gene, JAK2 (V617F) , was discovered in several myeloid proliferative neoplasms including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). Demonstration of the mutation and other similar mutations has now become one of the major criteria in the diagnosis of these neoplasms in the revised World Health Organization Classification of Tumors of Hematopoietic Tissues. In this chapter, we compared the advantages and disadvantages of five commonly used methods for the detection of JAK2 (V617F) . We explained, based on the current literature, why analytic sensitivity of the methodology is of particular importance for the detection of JAK2 (V617F) . A detailed laboratory procedure for the performance of an extensively optimized ARMS-PCR assay was presented. The assay shows distinct patterns for normal, mutant, and mixed genotypes. Diagnostically, it is highly sensitive, highly specific, and simple to perform with no need for any specialized equipment other than thermocyclers.