The global increase in the number of mass gatherings and crowded events has brought with it new emergencies and unintended consequences for public administrators and first responders. Crowd managers attempt to overcome these challenges by enhancing operations, alleviating financial losses, keeping event organizers safe from liability and, most importantly, keeping the attendees safe. Effective communication among and between officials and guests has been identified as a key element in this process. However, there is a lack of risk communication studies, especially about heterogeneous crowds that congregate at religious events. With this gap in mind, this research aims to investigate the use of major communication channels available and/or preferred by Muslim pilgrims in Makkah, Saudi Arabia during Hajj to gauge their effectiveness in communicating risk information. This annual religious pilgrimage was chosen because it attracts over 2 million pilgrims from more than 140 countries, most of whom speak different languages and belong to different cultures but perform the same rituals at the same time. This dissertation seeks to answer three broad research questions: “what are the most popular communication channels used by pilgrims,” “what are the weaknesses of the current communication strategies,” and “what can be done to improve risk communication …