Fannie Mae, or the Federal National Mortgage Association, guidelines are the minimum requirements you need to meet to take out a mortgage loan in the US housing market. Fannie Mae guidelines are important because they were developed to make the financing process less risky for both consumers and lenders. Fannie Mae buys individual mortgages from lenders, repackages them, and then sells them to investors in the secondary market. The corporation has different requirements for different loans. The minimum requirements may vary depending on whether the property is a multi-unit home, secondary home, or an investment property. Some Fannie Mae guidelines may include down payment requirements, credit score requirements, debt-to-income requirements, etc.