An employee stock purchase plan (ESPP) is a type of stock plan that permits employees to use after-tax payroll deductions to acquire shares of their company's stock. This differs from a 401(k) plan, to which money is contributed before income tax withholding. Plans can have different contribution rules and features, including discounts or company contributions (see a related FAQ).

The most common type of ESPP is known as a Section 423 plan, named after the part of the tax code that governs it. An ESPP that is tax-qualified under Section 423 ESPP offers favorable taxation of the purchase discount. Consequently, this type of ESPP is called a "qualified" ESPP (not to be confused with "qualified" retirement plans). Other types of plans are either nonqualified or direct purchase plans.

See a related article on all of the key dates and terms you must know before you participate in an ESPP.