This document is a guidance for industry regarding the development of drugs and biological products for rare diseases. It aims to assist sponsors in conducting efficient and successful drug development programs, acknowledging that the challenges faced in rare disease contexts often differ from those in common diseases. The guidance outlines various considerations, including the importance of understanding natural history studies, nonclinical studies, and clinical development aspects such as effectiveness and safety evaluations. It emphasizes the need for substantial evidence of a drug's effectiveness and safety for its intended use, while also recognizing the unique complexities associated with rare diseases. The document encourages early engagement with the FDA to address specific challenges in drug development for rare diseases, ensuring that sponsors can navigate the regulatory landscape effectively. Additionally, it highlights the potential for orphan-drug designation and associated incentives to facilitate the development of treatments for these conditions.