A mortgage loan or simply mortgage (/ˈmɔːrɡɪdʒ/), in civil law jurisdictions known also as a hypothec loan, is a loan used either by purchasers of real property to raise funds to buy real estate, or by existing property owners to raise funds for any purpose while putting a lien on the property being mortgaged. The loan is "secured" on the borrower's property through a process known as mortgage origination. This means that a legal mechanism is put into place which allows the lender to take possession and sell the secured property ("foreclosure" or "repossession") to pay off the loan in the event the borrower defaults on the loan or otherwise fails to abide by its terms. The word mortgage is derived from a Law French term used in Britain in the Middle Ages meaning "death pledge" and refers to the pledge ending (dying) when either the obligation is fulfilled or the property is taken through foreclosure. A mortgage can also be described as "a borrower giving consideration in the form of a collateral for a benefit (loan)".

Mortgage borrowers can be individuals mortgaging their home or they can be businesses mortgaging commercial property (for example, their own business premises, residential property let to tenants, or an investment portfolio). The lender will typically be a financial institution, such as a bank, credit union or building society, depending on the country concerned, and the loan arrangements can be made either directly or indirectly through intermediaries. Features of mortgage loans such as the size of the loan, maturity of the loan, interest rate, method of paying off the loan, and other characteristics can vary considerably. The lender's rights over the secured property take priority over the borrower's other creditors, which means that if the borrower becomes bankrupt or insolvent, the other creditors will only be repaid the debts owed to them from a sale of the secured property if the mortgage lender is repaid in full first.

In many jurisdictions, it is normal for home purchases to be funded by a mortgage loan. Few individuals have enough savings or liquid funds to enable them to purchase property outright. In countries where the demand for home ownership is highest, strong domestic markets for mortgages have developed. Mortgages can either be funded through the banking sector (that is, through short-term deposits) or through the capital markets through a process called "securitization", which converts pools of mortgages into fungible bonds that can be sold to investors in small denominations.

According to Anglo-American property law, a mortgage occurs when an owner (usually of a fee simple / freehold interest in real property, but frequently leasehold in England and Wales) pledges his or her interest (right to the property) as security or collateral for a loan. Therefore, a mortgage is an encumbrance (limitation) on the right to the property just as an easement would be, but because most mortgages occur as a condition for new loan money, the word mortgage has become the generic term for a loan secured by such real property. As with other types of loans, mortgages have an interest rate and are scheduled to amortize over a set period of time, typically 30 years in the United States. All types of real property can be, and usually are, secured with a mortgage and bear an interest rate that is supposed to reflect the lender's risk.

Mortgage lending is the primary mechanism used in many countries to finance private ownership of residential and commercial property (see commercial mortgages). Although the terminology and precise forms will differ from country to country, the basic components tend to be similar:

Many other specific characteristics are common to many markets, but the above are the essential features. Governments usually regulate many aspects of mortgage lending, either directly (through legal requirements, for example) or indirectly (through regulation of the participants or the financial markets, such as the banking industry), and often through state intervention (direct lending by the government, direct lending by state-owned banks, or sponsorship of various entities). Other aspects that define a specific mortgage market may be regional, historical, or driven by specific characteristics of the legal or financial system.

Mortgage loans are generally structured as long-term loans, the periodic payments for which are similar to an annuity and calculated according to the time value of money formulae. The most basic arrangement would require a fixed monthly payment over a period of ten to thirty years, depending on local conditions. Over this period the principal component of the loan (the original loan) would be slowly paid down through amortization. In practice, many variants are possible and common worldwide and within each country.

Lenders provide funds against property to earn interest income, and generally borrow these funds themselves (for example, by taking deposits or issuing bonds). The price at which the lenders borrow money, therefore, affects the cost of borrowing. Lenders may also, in many countries, sell the mortgage loan to other parties who are interested in receiving the stream of cash payments from the borrower, often in the form of a security (by means of a securitization).