In the US legal system, machine-generated proof is increasingly replacing human witnesses. Evidence such as geolocation data, machine-learning algorithms determining authorship of text, Fitbit app sleep data, and probabilistic genotyping software to prove DNA "matches" are already routinely offered as evidence of civil liability and criminal guilt. In the not-too-distant future, courts will grapple with medical diagnoses, lie detection, chatGPT answers, and other "expert" opinions offered by ever more advanced systems. But our legal rules related to witnesses are built for humans, not machines. For example, someone accused of a crime has a right to cross-examine, place under oath, and physically confront their accusers. But how do you cross-examine a machine? What does "confrontation" mean in an age of AI? This keynote address will discuss some of the ways courts and litigants are trying to adapt the legal system to these new realities, and ways that the biocomputing community can weigh in.