This paper describes the Terrier search engine, giving an overview of its architecture and main Information Retrieval (IR)
features, and reviewing the cutting-edge research implemented in it, with a special focus on Web search. IR research is con-
cerned with developing and evaluating search engines that retrieve relevant documents in response to a user query. Terrier is a
highly flexible, efficient, effective and robust platform for IR research, readily deployable on large-scale collections of docu-
ments [10]. Terrier implements state-of-the-art theoretically-founded models for IR, ranging from formal disciplines, such as
probability theory, statistics and natural language processing, to computational aspects of index compression and retrieval
efficiency. The research put into Terrier constantly expands towards new branches of the wider IR field, making Terrier a strong,
modular and state-of-the-art platform for developing and assessing new concepts and ideas.