库藏股，指的是公司将自己已经发行的股票重新买回，存放于公司，而尚未注销或重新售出。这样做可以减少市场上所有已发行股票的总数。在公司的资产负债表上，库藏股不能列为公司资产，而是以负数形式列为一项股东权益（Shareholder's Equity）。

库藏股的回购往往作为对股东的回报，但比直接发放红利更省税。公司在分析认为自己股票价格偏低时也往往会进行库藏股回购，作为一种融资手段。库藏股还可用于刺激与提高自己公司股票的交易量与股价。库藏股也可以用于提供公司内部的股票期权等员工福利。

库藏股与普通股相比有如下限制：

A treasury stock or reacquired stock is stock which is also bought back by the issuing company, reducing the amount of outstanding stock on the open market ("open market" including insiders' holdings).

Stock repurchases are used as a tax efficient method to put cash into shareholders' hands, rather than paying dividends, in jurisdictions that treat capital gains more favorably. Sometimes, companies do it when they feel that their stock is undervalued on the open market. Other times, companies do it to reduce dilution from incentive compensation plans for employees. Another motive for stock repurchase is to protect the company against a takeover threat.