This chapter addresses the concept and importance of marketability, and the penalties for lack of it and data quantifying average discounts for lack of marketability for minority interests. Marketability or liquidity is the ability to convert ownership interests to cash quickly, with minimum transaction costs and at a price very close to a known market price. This means that the investors can get their money whenever they want or need it. They do not risk being unable to sell during changing internal company or market conditions. Their proceeds are not diluted by high costs of finding a buyer and effecting a transaction. The chapter discusses evidence of the discounts for lack of marketability for minority interests. A large amount of empirical data is available to help quantify this discount for minority interests in closely held companies. The data fall into two major categories: trades in restricted or illiquid stocks of publicly traded companies; and trades in stocks of privately held companies prior to an initial public offering (IPO). The current restricted stock transactions somewhat less useful in determining private minority discounts. However, changes in the discount during the 1990s have shed light on the relative magnitude of marketability discounts as a function of the holding period and the degree to which the shares are restricted from resale. The pre‐IPO studies more closely represent the actual circumstances of a closely held company stockholder and thus are generally regarded as a better direct proxy for closely held company minority stock discounts for lack of marketability.