Previous research has not led to any agreement as to the normative trajectory of relationship satisfaction. In this systematic review and meta-analysis, we summarize the available evidence on development of relationship satisfaction, as a function of age and relationship duration. Data came from 165 independent samples including 165,039 participants. In the analyses, we examined cross-sectional information on mean level, that is, the percent-of-maximum-possible (POMP) score at the first assessment, and longitudinal information on mean change (i.e., change in POMP scores per year). The mean age associated with effect sizes ranged from 20 to 76 years and the mean relationship duration from 3 months to 46 years. Results on mean levels indicated that relationship satisfaction decreased from age 20 to 40, reached a low point at age 40, then increased until age 65, and plateaued in late adulthood. As regards the metric of relationship duration, relationship satisfaction decreased during the first 10 years of the relationship, reached a low point at 10 years, increased until 20 years, and then decreased again. Results on mean change indicated that relationship satisfaction decreased within a given relationship, with the largest declines in young adulthood and in the first years of a relationship. Moderator analyses suggested that presence of children and measure of relationship satisfaction explained variance in the mean level. Except for these two moderators, the pattern of findings held across characteristics such as birth cohort, sample type, country, ethnicity, gender, household shared with partner, marital status, relationship transitions, and dyadic data. (PsycInfo Database Record (c) 2022 APA, all rights reserved).