Hundreds of millions of people use online social networks (OSNs), and this use is growing rapidly. On the one hand, users of OSNs have created accounts, which include their personal information, interests, associations, postings, daily activities, sharing of social media, and so forth. In addition, users want to protect these information and activities. But on the other hand, they want to use the services, which are provided by OSNs in order to stay in touch with others. Therefore, for achieving this desire, users reveal their personal information intentionally or accidentally. Why? Because users of OSNs do not have adequate information that helps them in making security and privacy decisions effectively in addition to inadequate feedback about the implications of user decisions. This means users do not know what to reveal and how. In order to cope with this problem, a systematic literature review of the usable security and privacy on OSNs was performed. This review is an attempt to pursue the contours of research in OSNs. Therefore, this paper discusses the existing research work, highlights the main research challenges and existing solutions, identifies open research issues, and proposes some directions for future research in the usable security and privacy on OSNs.