A "lock-up agreement" is a contractual commitment between the underwriters and insiders of a company prohibiting these individuals from selling any shares of stock for a specified period of time after the company's public offering of securities. Lock-up periods typically last 180 days but can last for as little as 90 days or as long as 365 days, depending on the negotiations with the underwriters. Underwriters will often insist that officers, directors, and 1% or more shareholders of a company sign a lock-up agreement to ensure a measure of stability in a stock after it has been publicly offered.