In Maine, engagement rings are usually viewed as conditional gifts, that is, in the nature of a pledge for a contract of marriage.  Where no impediment exists to marriage and the recipient breaks the engagement, she is required upon demand to return the ring.[1]  However, if the engagement is broken by the donor or by mutual consent, the donee keeps the ring.

[1] O’BRIEN v. HUDOCK, 1984 Me. Super. LEXIS 146 (Me. Super. Ct. Aug. 30, 1984)