Machine ethics is concerned with how machines behave toward human users and other machines. It aims to create a machine that's guided by an acceptable ethical principle or set of principles in the decisions it makes about possible courses of action it could take. As ethics experts continue to progress toward consensus concerning the right way to behave in ethical dilemmas, the task for those working in machine ethics is to codify these insights. Eight articles in this special issue address the issues.This article is part of a special issue on Machine Ethics.