According to second-personal approaches to moral obligation, the distinctive normative features of moral obligation can only be explained in terms of second-personal relations, i.e. the distinctive way persons relate to each other as persons. But there are important disagreements between different groups of second-personal approaches. Most notably, they disagree about the nature of second-personal relations, which has consequences for the nature of the obligations that they purport to explain. This article aims to distinguish these groups from each other, highlight their respective advantages and disadvantages, and thereby indicate avenues for future research.