Can I invest in the stock market while I'm on an F-1 or OPT student visa?

Yes. There is no immigration rule barring F-1 or OPT students from owning U.S. stocks, ETFs, or mutual funds. Passive investing is not "work," so it doesn't violate your status the way unauthorized employment would. You can open a regular taxable brokerage account at Fidelity, Vanguard, or Schwab using your SSN (if you have one from on-campus work) or an ITIN. The catch is taxes: most F-1 students are nonresident aliens for their first five calendar years, which means capital gains may be tax-free but dividends are usually withheld at 30% (or a lower treaty rate). Keep good records and file Form 1040-NR. Start small with a low-cost index fund rather than day-trading. See wealthserene.com/for/immigrant-nri.