This is a clinical practice guideline for adults with newly diagnosed diffuse low grade glioma (LGG). Recommendations are drawn from the following three questions: what is the optimal role of external beam radiotherapy in the management of adult patients with newly diagnosed low-grade glioma (LGG) in terms of improving outcome (i.e. survival, complications, seizure control or other reported outcomes of interest); which radiation strategies (dose, timing, fractionation, stereotactic radiation, brachytherapy, chemotherapy) improve outcomes compared to standard external beam radiation therapy in the initial management of low grade gliomas in adults; and Do specific factors (e.g. age, volume, extent of resection, genetic subtype) identify subgroups with better outcomes following radiation therapy than the general population of adults with newly diagnosed low-grade gliomas. In addition to providing recommendations in response to these questions, the guideline also provides a discussion about key issues for future investigation. These issues include the development of novel molecular or genetic markers in low-grade gliomas, and utilizing imaging alternatives to standard MRI to assess tumor response.