Honesty is considered a core value for partners to close relationships and truth-telling far exceeds deception in such relationships. But close relationships inevitably involve confrontations about privacy, secrets, and the desire to avoid hurting a partner’s feelings. Sometimes, but not often, partners respond to such situations with lies. Deception in close relationships can be complicated because, among other things, the partners may mutually create and sustain a lie. Four principles characterizing close relationships provide a framework for understanding the production and detection of lies in close relationships—e.g., the frequency of interaction, the depth of knowledge about a partner’s behavior, a strong emotional investment in continuing the relationship, and the expectation that partners will recognize and respect each other’s vulnerabilities. Detection of lies in these relationships may be low due to the strength of the truth bias and the trust established or high because of context familiarity, knowledge of the other, and unlimited time to gather facts and evidence. While the consequences of discovered lies can be extremely detrimental to the relationship, many couples work through even the most destructive lies. When lies are uncovered, the critical factors related to its effect are: what the lie was about, its centrality to the relationship, and the likelihood of its recurrence.