The poor prognosis and high mortality for cancer patients are majorly ascribed to tumor metastasis, one of the most complicated pathological processes. Elucidation of molecular mechanisms for metastasis is essential for management and prevention of this lethal condition. In the book to be published, we take comprehensive review in regard with the signal mechanisms responsible for triggering a series of phenotypical changes of primary tumor which may lead to final colonization of the tumor in a second home. Specifically, the initial stage of tumor metastasis will be highlighted. The complex tumor microenvironment accumulate a lot of growth factors, inflammatory cytokines and extracellular matrix which may turn into a group of potent metastatic factors. An integrated and sustained signaling induced by these metastatic factors may trigger EMT, migration and invasion of primary tumor into surround tissue. Blokcade of these signal pathways is the most effective approach for prevention of tumor metastasis. A lot of clinical trials are under way for this purpose and the outcome are promising. The expert reviews compiled in this book may encourage the researcher in this exciting field for future study.