For many in the English-speaking world, Islam remains a mysterious religion. What is Islam in the first place? Does it mean peace, or does it mean submission? Can it mean both? What is jihad? Sharia? Hadith? Who is Allah? What is a caliph, caliphate, or infidel? In this compact volume, an expert in the study of Islam provides explanations for more than one hundred important Islamic concepts and terms, which are divided into major sections: texts, history, faith and belief, practice and religious duties, jurisprudence, and movements. Ayman Ibrahim first introduces the section, then defines each concept or term briefly. Readers can read a chapter at a time or flip through the book to find concepts or terms as needed. Each term is described based on original Muslim sources, mainly written in Arabic, as well as ample scholarly studies. This introductory guide is written for anyone with little to no knowledge of Islam. It complements the author's A Concise Guide to the Quran and A Concise Guide to the Life of Muhammad. Together, these three volumes are useful as a set of resources on Islam.