This book is appropriate for academic and practitioners who are interested in understanding Muslim interaction in online space. The book provides insight on how Muslim scholars have used online space for preaching activities in particular in Indonesia context. Many of Islam preachers become famous in short time and have million followers or viewers on social media sites. More and more Muslim enjoy religious preaching from online sources. This has created a new phenomenon in Islamic teaching delivery. At the same time, this phenomenon has also created new space for Muslim scholars and institutions to practicing research in online space to understand Muslim interaction in online space. Some strategies and benefits to practicing research in understanding Muslim in online space are discussed. However, few Muslim has also misused online space for radicalism activities, such as to recruit new members, solicit a donation, disseminate a radical ideology, etc. Readers who interested to understand Muslim activities in online space are encouraged to read this book.