A mutual friend is an individual who has established a friendship with two people. When those two people meet, they learn that they share the same friend; that friend they have in common is their mutual friend. If the two people become friends, a circle of friendship develops between the mutual friend and the other individuals. Mutual friendships are commonplace in schools, where kids are introduced to each other by a mutual friend. Adults often meet other people in the workplace, bars, restaurants and other social settings due to a mutual friend introducing them.

The concept of mutual friends extends to social networking as well. A mutual friend on the website Facebook is someone who is friends with a Facebook user and the person who's profile the user views. When visiting the Facebook profile of a person with whom you're not friends, the website displays a list of people who are that person's friends and your friends; they are mutual friends. The website Twitter similarly integrates a mutual friends list in its service. If you visit a person's profile on Twitter, the website lists the friends that you follow that also follow that person.

Mutual friendships serve as the foundation for many dating experiences. For example, two people dating may be compatible due to having a lot in common between themselves and with a mutual friend. Blind dates are occasionally set up by a mutual friend who believes his two friends are a good match for each other. If the blind date is disastrous, however, the mutual friend risks straining both of his friendships.

Mutual friendships are beneficial in making new friends. Creating an opportunity to meet your mutual friend's social circle is a way to develop new friends easily. The opportunity could be a party or other social event. According to a SucceedSocially.com article, the friends are "pre-screened for characteristics you like because they already know your friend." The mutual friendship nearly guarantees you will see your buddy's friends again. After repeated encounters, a friendship may develop naturally between you and your mutual friend's companions.