Metastatic liver tumors are more common than primary liver cancers and are the most common liver malignancies. Performing B-mode ultrasonography and contrast-enhanced computed tomography is generally necessary for the diagnosis of liver metastases. However, various modalities, including dynamic contrast-enhanced computed tomography and magnetic resonance imaging using liver-specific contrast agents such as gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid, fluorodeoxyglucose positron emission tomography, and a combination of positron emission tomography and computed tomography, are also used. Improvements in imaging technology have made the detection of small liver masses possible, and liver metastases are being diagnosed more frequently, both before and after primary tumor treatment. The diagnosis of liver metastasis is related to treatment, and the benefits of liver resection depend on the primary tumor. For colorectal cancer, resection of liver metastases is beneficial. However, resection is not recommended for pancreatic or biliary tract cancers.