The lungs are among the most prominent target organs for metastatic disease. Most frequently, lung metastases originate from cancers of the head and neck, breast, stomach, pancreas, kidney, bladder, the male and female genitourinary tract, and sarcomas. Plain chest radiography is typically the modality used for detection and therapeutic monitoring; however, the use of CT for these purposes is becoming more frequent. Currently, spiral CT appears to be the most sensitive imaging technique in the identification of metastases, because it detects a higher number of pulmonary nodules compared to other techniques. Pulmonary metastatic disease manifests itself by the presence of pulmonary nodules, lymphangitic carcinomatosis, endobronchial tumors, and pleural involvement. Nevertheless, the differential diagnosis is an important consideration, particularly in patients with solitary pulmonary nodules, systemic disorders, and signs or symptoms indicative of infection. The role of the radiologist involves the identification of metastatic disease, monitoring of response to therapy, and the use of invasive procedures when the differential diagnosis indicates the need for biopsy and histopathologic proof. The radiologist must be aware of the impact of his diagnosis on patient management and should be familiar with oncologic strategies as well as the terminology used to characterize tumor response. In future, the role of imaging may further expand due to the increased sensitivity in lesion detection, increased specificity in lesion (tissue) characterization using MR imaging imaging, and reduced radiation exposure.