货币基金，又称为货币市场基金（Money funds, Money market funds，or Money market mutual funds）是共同基金的一种，指投入现金定存以及高信用评等的短期票券（一般在1年以下）的基金。

一般而言这类基金所投入资产风险较小，极少出现本金亏损的情形，而被认为是资金的短期避风港。但在2007年－2009年环球金融危机中，因为一些公司的倒闭（例如雷曼兄弟）使得一些货币基金因购买了这些公司的短期票券而遭受损失。

货币基金的投入理由与定存类似，一般有几项，一是作为投资其他货币的管道。（有些币种本身的兑换自由度不够高）；二是在类似的风险波动下，获得比定存稍高的收益。（但如果基金的收费过高这项功能就无法彰显）；三、利用基金转换的功能，将其他放在股票、债券基金的资金，暂时转入货币基金，待机会再转换至想要投入的基金中。

A money market fund (also called a money market mutual fund) is an open-ended mutual fund that invests in short-term debt securities such as US Treasury bills and commercial paper. Money market funds are widely (though not necessarily accurately) regarded as being as safe as bank deposits yet providing a higher yield. Regulated in the United States under the Investment Company Act of 1940, money market funds are important providers of liquidity to financial intermediaries.