A relationship breakup, breakup, or break-up is the ending of a relationship. The act is commonly termed "dumping [someone]" in slang when it is initiated by one partner. The term is less likely to be applied to a married couple, where a breakup is typically called a separation or divorce. When a couple engaged to be married breaks up, it is typically called a "broken engagement". People commonly think of breakups in a romantic aspect, however, there are also non-romantic and platonic breakups, and this type of relationship dissolution is usually caused by failure to maintain a friendship.

Susie Orbach (1992) has argued that the dissolution of dating and cohabiting relationships can be as painful as or more painful than divorce because these nonmarital relationships are less socially recognized.

Kamiar-K. Rueckert argues with the works of Donald Winnicott that the ability to be alone is an essentially healthy sign of emotional development and maturity. Once a child has obtained closeness and attachment by their early caregivers, they are able to develop autonomy and identity. If children have not introjected the good and protective qualities of their parents, they will fear separation and break-ups.

Several psychological models have been proposed to explain the process of a relationship breakup, many suggesting that relationship dissolution occurs in stages.

Mark L. Knapp, a foundational scholar on the subject of interpersonal relationships, created a model called Knapp's relational development model. He describes two separate phases of relationships, coming together and coming apart.

The coming together phase is meant to be long-term, beginning in the initiation phase and becoming deeper with time and intimacy. In the coming apart phase, differentiating begins. This is when the individuals began noticing differences that may seem unnegotiable or place pressure on the relationship. This leads to circumscribing where the individuals begin to pull apart, set boundaries, and have their own independent lives. This may cause issues to arise. At this point, the relationship reaches stagnation where the couple stays together for other reasons rather than their will to do so. Examples include children. The next stage is avoidance in which the individuals try to stay away from each other as much as possible. They, then, reach termination, where the relationship is over and they go their separate ways.

L. Lee proposes that there are five stages ultimately leading up to a breakup.

Steve Duck outlines a six-stage cycle of relationship breakup: