What is the difference between a design patent and a utility patent?

Put simply, a design patent protects an article's design --its unique external appearance-- while a utility patent protects the article's function. Utility patents also cover certain subject matter as to which a design patent would not apply (like processes and chemical compounds).

In some cases, an invention may qualify for both design and utility patent protection. Since each is a distinct form of protection, the inventor would need to apply for both types separately, to take advantage of both forms of protection.