Primary and secondary liver tumours are common malignancies that are being treated more aggressively nowadays than decades ago. Surgery is the most effective method of treatment but is only suitable for a minority of patients with well-defined and easily accessible tumours. Surgical resection is contraindicated in patients with massive involvement of the liver or in cases where the disease involves the confluence of vessels at the porta hepatis. These patients may benefit from a variety of ablative and embolic therapies including selective internal radiation therapy (SIRT) with Yttrium-90 microspheres. SIRT has been introduced in the 1980s but the technology has been refined and made more available only recently. The microspheres are injected directly into the hepatic arteries, through a trans-femoral angiographic approach, and are delivered selectively to tumours due to their preferential blood supply by hepatic arteries. SIRT can therefore target small volumes disease with a higher dose of radiation compared with external-beam radiation and is associated the relatively low toxicity and a good response irrespective of tumor origin. Assessment of response to therapy is best performed with metabolic imaging using 18F-FDG PET scanning. Although it is not considered as a cure, it has been shown to improve quality of life and prolong survival, with the main cause of death being extra-hepatic spread. The technical and clinical demands of patient selection, treatment planning, administration, and clinical follow-up require an interdisciplinary team willing to work cooperatively to achieve the best result for the patient.