This open access book constitutes the proceedings of the 20th International Conference on Agile Software Development, XP 2019, held in Montreal, QC, Canada, in May 2019. XP is the premier agile software development conference combining research and practice. It is a hybrid forum where agile researchers, academics, practitioners, thought leaders, coaches, and trainers get together to present and discuss their most recent innovations, research results, experiences, concerns, challenges, and trends. Following this history, for both researchers and seasoned practitioners XP 2019 provided an informal environment to network, share, and discover trends in Agile for the next 20 years The 15 full papers presented in this volume were carefully reviewed and selected from 45 submissions. They were organized in topical sections named: agile adoption, agile practices; large-scale agile; agility beyond IT, and the future of agile.

The "Bell Curve" by Richard J. Herrnstein and Charles Murray has generated a firestorm of debate, confirming for some their secret belief in the innate inferiority of certain "races" or ethnic groups, angering many who view the book as an ill-concealed racist manifesto, and worrying untold others who fear the further racial polarization of American society. In "The Bell Curve Wars," a group of our country's most distinguished intellectuals dismantles the alleged scientific foundations and criticizes the alarming public policy conclusions of this incendiary book.Anyone who has wondered about the connection among genes, race, and intelligence, all those anxious about racial antagonisms in our nation, those who question the efficacy of social welfare programs, all those troubled but unconvinced by Herrnstein and Murray's book, will want to read "The Bell Curve Wars."