This research describes perceived rules pertaining to honesty in romantic relationships, identifies sources of accuracy and bias affecting consensus on rules, and clarifies implications for couple conflict. Couples typically idealize honesty; yet, situational rules are vulnerable to different interpretations due to ambiguous properties of deception and pressures to balance openness with discretion. The research distinguishes obligatory rules, which prescribe disclosure or proscribe deception, and discretionary rules, which grant flexibility. Couples agreed on obligatory rules more than discretionary rules, although females endorsed obligatory rules more than males. Individuals overestimated agreement, overattributed sex-stereotypic rule endorsement to the partner, and showed minimal understanding of expectations unique to the partner. Agreement on obligatory rules was associated with lower conflict, whereas understanding predicted greater conflict.