This book constitutes the refereed proceedings of the 11th Information Retrieval Societies Conference, AIRS 2015, held in Brisbane, QLD, Australia, in December 2015. The 29 full papers presented together with 11 short and demonstration papers, and the abstracts of 2 keynote lectures were carefully reviewed and selected from 92 submissions. The final programme of AIRS 2015 is divided in 10 tracks: Efficiency, Graphs, Knowledge Bases and Taxonomies, Recommendation, Twitter and Social Media, Web Search, Text Processing, Understanding and Categorization, Topics and Models, Clustering, Evaluation, and Social Media and Recommendation.