The concept of 'negative concord' refers to the seemingly multiple exponence of semantically single negation as in You ain't seen nothing yet. This book takes stock of what has been achieved since the notion was introduced in 1922 by Otto Jespersen and sets the agenda for future research, with an eye towards increased cross-fertilization between theoretical perspectives and methodological tools. Major issues include (i) How can formal and typological approaches complement each other in uncovering and accounting for cross-linguistic variation? (ii) How can corpus work steer theoretical analyses? (iii) What is the contribution of diachronic research to the theoretical debates?