A Section 83(b) election is applicable when a substantial risk of forfeiture exists in the underlying shares of an equity grant. In privately held companies, an 83(b) election is made upon an exercise of stock options or a grant of stock ONLY if the shares you get must vest before they become yours to sell or transfer. For details, see this website's section on early-exercise stock options.

In limited situations, stock subject to a company buyback or repurchase right is considered to have a substantial risk of forfeiture. Although the SEC imposes restrictions on resales of private company stock, they are not involved in this share-vesting requirement.

Alert: You do not need to file an 83(b) election for standard stock options that you can exercise only after vesting, as the stock received at exercise is not subject to a substantial risk of forfeiture. Also, don't confuse restricted stock or restricted stock units with restricted securities, which are something different (shares in a private company that are not registered with the SEC and are not easy to sell). They also do not require a Section 83(b) election at exercise.