This Open Access book is the first comprehensive guide to identifying antisemitism online, in both its explicit and implicit forms. Developed through years of on-the-ground analysis of tens of thousands of authentic web comments the book maps out and deconstructs, with concrete examples, more than 45 key antisemitic concepts. The guide was assembled by researchers working on the Decoding Antisemitism project at the Centre for Research on Antisemitism at Technische Universität Berlin, building on and extending existing definitions of antisemitism, and drawing on expertise in the fields of conceptual history, antisemitism studies, linguistics, discourse and image studies, and social media studies. Using authentic examples taken from social media discussions over the past five years, it develops a pioneering step-by-step approach to identifying and categorising antisemitic content, providing guidance on how to recognise a statement as antisemitic or not. It shows how to establish whichantisemitic concept a statement expresses, and the linguistic or visual means by which it is communicated. This book will be an invaluable tool for researchers, students, practitioners in education, police, justice, NGOs and politics, and social media moderators to learn to recognise contemporary antisemitism in all its breadth and diversity. It also establishes a framework which can be adapted by those working on other hate ideologies, including misogyny, racism, and homophobia.