U.S. patents include three types: inventions, designs, and new plant varieties. U.S. invention patent: 20 years from the date of application, maintenance fees shall be paid three and a half years, seven and a half years and eleven and a half years from the date of registration respectively. The validity period of a patent covering a composition or a method of using the composition may be extended by up to 5 years. U.S. design patent: fourteen years from the date of registration. A patent application can still be filed within six months after publication (this is a major difference between the novelty judgment of US patents and Chinese patents). New plant variety patent: 20 years from the date of application, maintenance fees shall be paid three and a half years, seven and a half years and eleven and a half years from the date of registration respectively.