The wedding ring effect—or mate-choice copying in humans—is the notion that individuals, particularly women, have a greater preference for those who are currently involved in romantic relationships as their partners over uninvolved individuals. This book provides a thorough, critical review of previous research on the wedding ring effect and presents a study that examined two manipulated independent variables of romantic targets (i.e., relationship availability and openness to commitment), as well as one independent individual difference variable of participants (i.e., sociosexuality), in order to better understand the underlying mechanism of the wedding ring effect. The results revealed that a target’s high level of commitment, regardless of his availability, increased both his likability and romantic attractiveness for restricted maters. For unrestricted maters, neither target availability nor commitment had a significant effect on their liking or attraction. These findings appear to discredit the notion of the wedding ring effect and highlight the importance of target commitment and the moderating role of individual difference in women’s mate preference.