A condolence letter is a piece of correspondence sent to someone to express condolences for a death. Condolence letters are classically sent to the lead mourner, although they can also be sent to the extended family and friends of the deceased. A condolence letter differs from a condolence card in length, with condolence letters being more detailed and personalized.

People usually send condolence letters when they have a deep personal connection with the deceased or the mourners. Condolence letters typically include an expression of condolences, followed by a discussion of the life and actions of the deceased, and many people include brief memories or vignettes about the deceased which are designed to illustrate the richness or his or her life. Typically, condolence letters convey a deep appreciation for the personality and life of the deceased, along with offers of assistance to the mourners. At the close of the letter, an additional expression of condolence and support is included.

Typically, a condolence letter is written within two weeks of a death. It is written on formal and simple stationery, and written out by hand, rather than being typed. Typed letters and emails are usually frowned upon by etiquette experts, because of the impersonality of typing. The condolence letter is also personalized to the deceased, with specific references to his or her religious faith, beliefs, personality, and life.

Mourners greatly appreciate condolence letters, although they may not always be able to respond to them. Many people keep condolence letters as mementos, and they especially enjoy letters which include personal stories or information about the deceased. References to ways in which the deceased influenced the life of the letter-writer are also common in a condolence letter, as a way of letting the mourners know that the life of the deceased had value, and that the deceased had an impact on someone's life.

A condolence letter is simply one way of giving condolences, but it is often a very valuable way to extend sympathy and love to mourners, since it can be kept and treasured, unlike a visit or a gift of flowers. Inclusions of photographs and mementos belonging to the deceased can also personalize a condolence letter, and provide something for the mourners to reference when thinking about the deceased. In addition to sending a condolence letter, people who live near the mourners may also attend the funeral or visit the home of the mourners to pay a personal condolence call.