An 83(b) election allows founders and employees to pay taxes on their restricted stock and early exercisable stock options before they vest. Paying taxes early with an 83(b) election can potentially reduce taxes significantly.

For restricted stock (RSAs), you must file your 83(b) election within 30 days after the grant date of your restricted stock.

For stock options with early exercise provisions, you must file the 83(b) election within 30 days of early exercising. You can early exercise at any time before the options vest.

You can find instructions and a downloadable template here. Unfortunately, as of July 2020, there is no way to submit the election online; it must be mailed in.