Preface The second execution of the Social Media Mining for Health Research and Applications (SMM4H) workshop was held in Washington D.C. (United States) on November 4, 2017, co-located with the American Medical Informatics Association (AMIA) Annual Symposium 2017. The workshop, which included a shared task component and a research forum component, followed its first successful implementation at the Pacific Biocomputing Symposium, 2016. The aim of the SMM4H workshop was to provide a forum for the AMIA community members to present and discuss advances in social media mining for the broader health domain. The workshop sought to attract researchers interested in automatic methods for the collection, extraction, representation, analysis and validation of social media data for health informatics, including epidemiological and behavioral research applications. The overarching goal of the SMM4H series is to bridge the gap between the advances in social media mining and the practical needs of healthcare and public health monitoring practitioners. This volume of workshop proceedings includes 16 long and short papers, including 10 system descriptions. Each paper in the proceeding was peer reviewed. 9 papers from the proceedings were chosen for oral presentation at the workshop. The papers published in this volume cover an assortment of topics including natural language processing, image processing, machine learning and corpus curation, and the applications of these methods and resources in practice. We would like to thank the co-organizers, program committee members, authors and all shared task participants for their contributions. Based on the success of this workshop, we look forward to organizing the next iteration of this workshop in 2018. Chairs of the SMM4H 2017 Workshop Abeed Sarker Michael J. Paul Graciela Gonzalez Workshop Chairs Abeed Sarker (University of Pennsylvania) Michael J. Paul (University of Colorado-Boulder) Graciela Gonzalez (University of Pennsylvania) Additional Organizing Committee Members Nigel Collier (University of Cambridge) Azadeh Nikfarjam (Stanford University) Cecile Paris (CSIRO, Australia) Pierre Zweigenbaum (CNRS, France) Additional PC Members Ari Z. Klein (University of Pennsylvania) Masoud Rouhizadeh (University of Pennsylvania) Davy Weissenbacher (University of Pennsylvania) Arjun Magge (Arizona State University) Tasnia Tahsin (Arizona State University)