The editors selected topics most relevant to clinical practice in order to provide a useful guide for practicing physicians. Chapters describing four disorders (T-cell large granular lymphocytic leukemia, chronic lymphoproliferative disorder of NK cells, extranodal NK cell lymphoma and aggressive NK cell leukemia) incorporated into most recent 2016 revision of classification of lymphoid malignancies are separated into experimental, diagnositc and clinical parts for easier understanding and reading. We are aware of challenges and inherited limitations of any larger project like this one due to a rapid progress especially in the field of genomics, which may not be incorporated in this book before it is published. The editors and contributing authors would like to thank the publisher NOVA for their support. (Nova Biomedical)