市值指一间（或一组）上市公司在证券市场上的「市场价格总值」的简称。

一般会以有关上市公司在相关证券市场上的收市价格作为计算基准，乘以其已发行的股份总数，而得出的市场价格总值。

由于市值的计算基准为有关上市公司的收市价，因此数字会随股价升降而变动，而市值的升降，亦反映投资市场的买卖气氛，及对有关公司的最新估值。

例子：某上市公司于1月1日在交易所的收市价为15元，而当天该公司的已发行股数为1,000,000,000股普通股（并无其他类别股份发行）；因此，该公司当天市值为15,000,000,000元。

Market capitalization (market cap) is the market value at a point in time of the shares outstanding of a publicly traded company, being equal to the share price at that point of time times the number of shares outstanding. As outstanding stock is bought and sold in public markets, capitalization could be used as a indicator of public opinion of a company's net worth and is a determining factor in some forms of stock valuation.