This chapter focuses upon the design of an opt-out class action. Not all design matters will be encapsulated in statute. Some will be contained in court rules, and some will not be included in legislation at all, but will be for case-by-case judicial precedent to establish in the courtroom. The chapter sets out a hundred design points, over the four stages of a class action: its commencement, its conduct, its ending via either settlement or trial, and the costs and funding issues that typically pertain to class actions litigation. By way of an illustrative case study, the chapter also cites several areas of class actions design in which the experiences garnered from over a quarter of century of Australian jurisprudence was useful for the lawmakers for the United Kingdom.