A life partner is a term commonly used to describe an intimate relationship between two people. Specifically, this term refers to a bond by which both individuals involved in the relationship commit to continue in the same relationship for a lifetime. A life partner may be a person of the opposite sex or of the same sex. Contemporary use of this term, however, is most commonly applied to same-sex relationships.

Cohabitation between life partners is common in many parts of the world. In countries such as the United States, Sweden, France, Denmark, Norway and Germany, legal recognition of some form is offered to partners who are committed to living together for life. Such recognition may be granted in the form of marriage, a domestic partnership or a civil union.

Life partners of the same sex often live together without a formal legal arrangement or may choose to form a civil union or a domestic partnership depending on the laws governing the jurisdiction where both partners reside. In some jurisdictions, same-sex partners may also be allowed to legally wed. Though partners in a heterosexual marriage are commonly referred to as husband and wife, spouses in a heterosexual marriage are in a life partner relationship.

In varying forms, legal status is sometimes offered to life partner relationships to protect individuals and families in the event that one partner falls ill or dies. Legal status applied to these relationships is also helpful in deciding legal disputes over property and assets in the event that one or both partners choose to end the relationship. In some situations where a partnership involves a same-sex couple not allowed to marry civilly, the rights that accompany a domestic partnership or civil union are intended to act in a similar manner to the legal rights that accompany heterosexual civil marriage.

Often used to describe a relationship between same-sex couples, a life partner does not necessarily have to be of the same sex. Heterosexual couples often commit to life partnerships, particularly when choosing to live together and have children together without registering for a civil marriage. While commonly used in describing romantic relationships, life partnerships may also be used to describe extremely close platonic friendships that are not characterized by romantic feelings or a sexual relationship.