When we first started studying CEO activism three years ago we never imagined how significant this phenomenon would become.

At the time a small but growing band of executives were taking public stands on political and social issues unrelated to their companies' bottom lines. Since then, controversies over laws affecting transgender people in North Carolina, police shootings in Missouri, and executive orders on immigration have drawn increasing numbers of CEOs into contentious public debates. More recently, the White House's withdrawal from the Paris climate accord, response to the clash between white supremacists and counterprotesters in Charlottesville, Virginia, and decision to rescind Deferred Action for Childhood Arrivals have galvanised many US corporate leaders to speak out and take action.