A large proportion of relationships that go through a growth and development trajectory will, at some point, reverse and deteriorate. This deterioration can be either abrupt or long and drawn out; furthermore, it can be either temporary and later repaired or irrevocable and result in a permanent breakdown of the relationship. Because the dissolution of close relationships is one of the most painful human experiences, and one that can also have costs for society, it has received the attention of scientists from a variety of disciplines. Research on relationship dissolution has focused on three major issues: (1) What causes relationships to break up? (That is, why does one relationship endure and another end?) (2) What is the process by which relationships end? and (3) How do people respond and cope after a breakup? This brief chapter can only touch the surface of the voluminous literature on the breakup (vs. the stability) of marriages and other close relationships. In the first section, we describe types of dissolution. The second section is a review of the causes of relationship (in)stability, both from the researcher's perspective and from the perspective of those who suffer through a breakup. In the final section, we discuss the process and aftermath of relationship dissolution.