Successful participation in the legal system depends to a considerable extent on the ability to manipulate language. Many people who are usually very fluent and articulate speakers feel that they are at a disadvantage in the legal process, because of such factors as the use of complicated legal terms (see Legal-Professional Language in Jury Trial), the asymmetrical power relations between legal professionals and other participants, and the often serious consequences of the legal matters in which they are involved. Yet, it is clear that some people are more vulnerable than others in the legal process, and to define this vulnerability necessarily involves a consideration of sociolinguistic issues because of the centrality of successful language use to successful outcomes in legal contexts. This article begins by looking at participants in the legal system who are vulnerable because of enduring aspects of their social identity, such as native language variety and age, and concludes by looking at those whose vulnerability is due primarily to their situated identity in the legal matter in which they are participating; for example, victim-witnesses. Although this article defines vulnerable participants in sociolinguistic terms, it is important to point out that a number of governments around the world have formally defined vulnerable witnesses as part of the process of enacting special measures to assist them in coming to court, understanding the process, and giving evidence. For example, such witnesses may be permitted to give direct evidence from a separate room via closed-circuit television. In the terms of such provisions, vulnerable witnesses are usually defined foremost as children, and the category often also includes people with mental, learning, and sometimes physical disabilities. It may also include intimidated witnesses, such as survivors of abuse. In some jurisdictions, such as the Northern Territory of Australia, the status of vulnerable witness is extended also to people who experience difficulty related to linguistic or cultural difference. The sociolinguistic view of 'vulnerable participants' used in this article corresponds to the most inclusive of the various legal definitions.