Flow cytometry immunophenotyping of hematopoietic disorders is a complex and demanding exercise that requires a good understanding of cell lineages, developmental pathways, and physiological changes, as well as broad experience in hematopathology. The process includes several interrelated stages, from the initial medical decision regarding which hematologic c- dition is appropriate for FCM assay, to the final step of diagnosis whereby the FCM data is correlated with other relevant clinical and laboratory information. The actual FCM testing involves three major steps: pre-analytical (specimen processing, antibody staining), analytical (acquiring data on the flow cytometer) and post-analytical (data analysis and interpretation). The literature, including the latest FCM textbooks, provides ample information on the te- nical principles of FCM such as instrumentation, reagents and laboratory methods, as well as quality control and quality assurance. Similarly, correlations of morphologic findings and p- notypic profiles have been well covered in many publications. In contrast, much less attention has been given to the other equally important aspects of FCM immunophenotyping, especially data analysis. The latter is a crucial step by which a phenotypic profile is established. To bridge this gap in the literature, the focus of this book is more on FCM data analysis than laboratory methods and technical details. For the reader to become familiar with our data analysis strategy, an overview of our approach to the pre-analytical and analytical steps is also presented, with an emphasis on the pre-analytical aspects, which have been rarely touched upon in the literature.