Lung carcinomas frequently metastasize to other organs. Metastasis is the most common cause of death in lung cancer patients. In this chapter, we will focus on two different aspects: the Mechanisms of metastasis of lung carcinomas and the metastasis to the lung by other malignant tumors. Metastasis has to be dissected in different steps: migration, angiogenesis, hypoxia, microenvironment, creating immune tolerance, circulation, extravasation, establishment of a metastatic focus, and finally, cross talk with the new environment to facilitate tumor growth.