Metastasis is an complex process by which tumor cells travel through various parts of body where they begin to grow and form new tumors that replace the normal tissue. Metastasis unequivocally marks a tumor as malignant because benign neoplasms do not metastasize. The invasiveness of cancers permits them to penetrate into blood vessels, lymphatics and body cavities providing the opportunity for spread. Metastasis is of great importance to the clinical management of cancer since the majority of cancer mortality is associated with disseminated disease rather than the primary tumor. This book emphasises on different modes of metastasis which in turn says about aggressiveness of tumours as they play an important role for prognosis of tumours.