What is Form 8843 and do I have to file it as an F-1 student with no income?

Form 8843 is the IRS statement that F, J, M, and Q visa holders file to document that they're exempt individuals whose U.S. days don't count toward the substantial presence test. You must file it every year you claim the exemption, even if you had zero U.S. income and owe no tax; it's how you preserve your nonresident status and your five-year student clock. If you had income, you attach it to your Form 1040-NR; if you had none, you mail Form 8843 by itself by the deadline. Missing it can jeopardize your exempt-individual claim. The IRS explains Form 8843 and exempt individuals in Publication 519 at irs.gov.