This volume gathers contributions from the final workshop of the RILEM TC-251-SRT "Sulfate Resistance Testing" on External Sulfate Attack (TESA 2018), held on May 24-25, 2018 at IETcc-CSIC, Madrid, Spain. One of the Technical Committee's main events, it addressed various aspects of external sulfate attack in concrete structures and test methods. The workshop promoted technical discussions and debates on ideas on these topics, with a focus on evaluating the resistance of concrete exposed to ESA. It also provided a forum for participants from around the globe to share their experiences and research on concrete structures affected by external sulfate attack and on test methods. The book discusses the latest advances in research related to ESA and new developments in test methods, and features real-world case studies of concrete structures affected by external sulfate attack in various countries. It also presents new studies linking field cases and lab tests, including 12 contributions on3 main themes: mechanisms of alteration in external sulfate attack; field aspects of external sulfate attack; and testing to evaluate the resistance of concrete to external sulfate attack.