The section of the Internal Revenue Code that determines what and when compensation for personal services is included in gross income. In the context of restricted stock and early-exercise stock options, income is not recognized while the stock is subject to a risk of forfeiture (e.g. vesting) unless a Section 83(b) election is filed with the IRS within 30 days of either (1) grant in the case of restricted stock or (2) exercise in the case of early-exercise options.