As the definition of palliative-intent radiation therapy (RT) continues to evolve, the application of advanced radiotherapeutic technologies, such as intensity-modulated RT, and techniques, such as image-guidance, are no longer the provision solely of the curative realm. Treatment options previously considered strictly palliative are expanding, with conventional RT being delivered in conjunction with other modalities such as highly conformal radiation, surgery or systemic therapy, or being bypassed entirely. Additionally, as the median survival rate for many primary cancer histologies improve, more and more patients are outliving the palliative benefit of their first course of RT, making re-irradiation a commonly encountered scenario. Many factors should be taken into account when making RT treatment decisions, including those incorporating advanced technologies, such as individualised considerations of symptom burden, extent of disease, life expectancy, performance status, comorbidities, toxicity, prior treatment, and patient wishes. However, while palliative RT should be appropriately customised for each patient, it should also have a convincing evidence base. To date, research investigating the optimal use of palliative RT has been strikingly underrepresented, especially considering it comprises up to 50% of a department's workload. This book reviews state of the art in palliative radiation therapy across all disease sites, discussing available evidence supporting the use of advanced technologies and related clinical and dosimetric outcomes. Areas in which practice diverges from available evidence, as well as those in which no supporting evidence exists, are described. Many chapters include a historical overview highlighting lessons learned from past experience and techniques. Additionally, where specific palliative literature does not exist, generalisable excerpts from the curative setting are examined as well. Also, key practice points pertinent to management approaches and decisions, treatment planning and other clinical pearls are summarised by over 60 international experts from three continents, often incorporating a multinational and/or multi-institutional perspective. A foundational chapter reviewing these technologies is complimented by sections on their use in each primary cancer site, along with chapters focusing on emerging techniques such as stereotactic radiation, clinical settings such as oligometastases, and patient-reported outcomes including quality of life and toxicity. Clinical trial methodology applicable to palliative RT, prognostication, health services research, and the interface of radiation oncology with palliative care in the 21st century are highlighted. Finally, a concluding chapter provides an overview of clinical contexts in which conventional radiation therapy or best supportive care may be favoured.