Volume 217, Issue 11, Pages 1025-1222 (November 2012) The XXIV International Complement Workshop (ICW) on October 10–15, 2012, on the scenic island of Crete, Greece, will serve as a timely and lively scientific platform to share the latest research updates and discuss emerging trends and concepts in the complement field. In addition to promoting research advancements, the ICW has been an important venue to tie the complement scientific community and create a nurturing home for established as well as young scientists where one can meet current or future collaborators and get inspired by new ideas. The ICW first started in 1963 as a two-day workshop held at the National Institutes of Health, Bethesda, MD (Science 141:738–740). Sponsored by the Immunology Section, Diagnostic Research Branch, of the National Cancer Institute, the inaugural meeting focused on complement and hemolysis and also discussed nomenclature issues. Whereas in the 1960s about 30 abstracts were presented per meeting, the number of oral and poster presentations have approached to 300 in recent years, thereby impressively reflecting the dramatic changes and exciting developments the field of complement research has experienced. Driven by seminal discoveries ranging from molecular to clinical aspects, and fueled by recent progress in the therapeutic intervention in complement-mediated diseases, novel insights into the function of complement appear at an increasingly rapid pace in leading biomedical journals. New players in the complement network have been discovered and several functional aspects have been redefined or extended, recently. Moreover, not only does complement live up to its name but proactively orchestrates immunological and inflammatory processes, extending far beyond simple elimination of pathogens. Research over the past decade has uncovered crosstalk and interconnections of complement with immunity at large and other physiological systems. We now have a good understanding of how complement acts as an intricate immune surveillance system, which discriminates among healthy host tissue, cellular debris, apoptotic cells and foreign intruders and tunes its response accordingly. As the complement network is positioned “upstream” of and is highly intertwined with a variety of bodily systems, it comes as no surprise that deregulation in the sensing or its effector functions can lead to disorders that are not necessarily or directly related to host defense against infection, but may include inflammatory and degenerative pathologies. The new trends, emerging topics, and paradigm shifts are appropriately reflected in the scientific program of the XXIV ICW. This includes oral and poster presentations on the genetics, structure and functions of complement, host–microbe interactions, complement crosstalk with other systems, and complement therapeutics and diagnostics pertaining to its multifaceted roles in pathophysiology. This Special Issue also hosts selected review articles from leaders in the field who have discussed exciting new findings placing the complement network at the heart of biological processes that influence human health and disease. We confidently anticipate open and vivid scientific discussions and the integration of new research ideas and talents, which together can further drive complement research to new horizons. Our sincere thanks to Prof. Wilhelm Schwaeble and the editorial staff of Immunobiology for their help and supervision in the production of this special issue, as well as to the contributing authors and reviewers for their time and effort in writing and reviewing the reviews hosted in this issue. Finally, we would also like to thank Rodanthi Lambris for collating and editing the abstracts and Dimitrios Lambris of Conferex LLC for managing the organization of this meeting.