Context: As of November 2021, GitHub reports having over 73 million users, more than 200 million repositories (28 million of which are public). It is the largest host of source code as of November 2021 and widely regarded as the most popular platform for social coding, offering its users a variety of different features including a pull-request based workflow, issue tracking and channels for communication. Communication is an essential part of successful collaboration in software development teams to organize and coordinate tasks and there has been a lot of work regarding communication in software projects in general. Problem: Due to the volume of information and results available, it becomes more and more important to provide an overview to summarize and highlight the more relevant aspects of the research area. Objective: The main objective of this thesis is to gain insight in the work about communication in GitHub projects over the years, identify the areas of interest in relation to the challenges, their proposed solutions and to summarize the state-of-the-art so far. Method: We conduct a systematic mapping study following all protocol and documentation details analyzing 38 of 507 publications from 2013 to 2021. Result: We present our answer to four research questions, a systematic map concerning the current challenges and solutions on the subject of communication in GitHub project and a variety of topic-independent statistics on the relevant publications in recent history. In addition, we describe the methods that stem from the frame of systematic mapping studies that we have employed to gather and evaluate the data. Conclusion: Our results indicate that the biggest challenge stems from problems regarding the user behaviour followed by user experience while at the same time the most prevalent solution is for the user to adjust their behaviour either to adapt to the given tools or by seeking to supplement with alternatives. This might indicate the shifting of responsibility of improving the circumstances for optimal communication towards the user as opposed to the available tools and functionalities instead. Furthermore, there appears to be a possible upward trend in this field of research. We hope that our results can act as a precursory foundation to navigate the topic of communication in GitHub projects to give information that can act as possible starting points for further reading.