The regulations for the classification of medical devices in the United States are based on risk assessment and intended use. Devices are categorized into three classes:

1. Class I: Low-risk devices that do not require premarket approval. Examples include tongue depressors and elastic bandages.

2. Class II: Moderate-risk devices that require special controls to ensure safety and effectiveness. Most require a 510(k) premarket notification.

3. Class III: High-risk devices that necessitate premarket approval based on scientific evidence demonstrating safety and effectiveness.

Classification is determined by comparing a device to legally marketed devices and evaluating factors like intended use, technology, and potential risks. Regulatory requirements vary by class and include labeling, manufacturing standards, and post-market surveillance to maintain safety standards throughout the device's lifecycle.