The “marriage effect” is one of the most widely studied topics of life course criminology. The contemporary consensus is that marriage promotes desistance from crime. Most of the 58 studies reviewed here find a negative longitudinal association between marriage and crime. The results are more consistent among men. Studies that attend to relationship quality, such as the level of marital attachment, tend to produce particularly strong associations. Critical scrutiny of the evidence regarding the causal nature of the reported associations suggests, however, that claims about the restraining influence of marriage are overstated. None of the studies demonstrates evidence of direct (counterfactual) causality; no study has served a causal estimate unbiased by selection processes. Moreover, only a few studies address time ordering, and some of those show that desistance precedes rather than follows marriage. Evidence in support of the theoretical mechanisms responsible for the marriage effect is also mixed and insufficient. The criminological literature has been insensitive to the reality that entering a marital union is increasingly unlikely to signify the point at which a committed, high-quality relationship is formed.