In almost all cases when applying for a paper visa (non electronic) your actual passport must be submitted. The visa will be stamped or placed onto one of the blank visa pages in your passport.
Please note that when applying for a visa your passport in most cases must be valid six months past your departure date. Additionally, the back three pages of US passports are amendment pages and no visas can be issued on them. If your passport is about to expire or you do not have any blank visa pages view the passport section of our website for assistance and requirements.
Some countries will issue an "e-visa" to some passport holders. In that case, you would apply for your visa online and your actual passport would not be required.