Non-specific orbital inflammation (NSOI) is a non-infectious orbital inflammation. Although it is often considered the most common diagnosis in orbital biopsies, it is an exclusionary diagnosis that requires ruling out systemic disease or other possible causes. Its characteristics include acute orbital signs and symptoms, including pain, proptosis, periorbital edema, chemosis, diplopia, and visual impairment. The clinical manifestations and histological findings of NSOI are heterogeneous, without specific diagnostic criteria or treatment guidelines, which poses significant challenges for diagnosis and treatment. This guideline provides a detailed description of the definition, classification, diagnosis, and treatment of NSOI.