This chapter introduces the idea of trial in absentia and serves as the starting point for the next four chapters of the book. It separates trial absences into four categories: 1) trial in absentia; 2) trial by default; 3) absences occurring after the start of trial; and 4) situations in which physical presence does not equate to actual presence. This chapter specifically considers trial in absentia, defined as a trial occurring entirely in the absence of the accused where the accused knows the trial is taking place but chooses not to attend. It predominantly discusses the issues of notice and waiver and the role they play in ensuring that the accused’s absence is voluntary. It finds that international criminal law permits the accused to voluntarily waive his or her right to trial but only if he or she has first received notice of the proceedings in a sufficient amount of time to allow him or her to adequately prepare a defence to the charges against them. Additionally, while notice can be express or implied, it must be unequivocal and clearly indicate that the accused wants trial to take place without his or her participation. It then examines the limited instances of trial in absentia conducted by international and internationalised criminal courts and tribunals to determine whether the accused properly waived his or her right to be present before trial continued in their absence.