This chapter examines the legal and practical issues encountered by practitioners when dealing with unfitness to plead litigation. As the Law Commission for England and Wales has pointed out, defendants charged with a criminal offence may be unfit to plead or to stand trial for a variety of reasons, including difficulties resulting from mental illness, learning disability, developmental disorder, or communication impairment. Two issues are considered: (i) how might those defendants who are unfit be accurately identified; and (ii) what steps should be taken by legal practitioners and by the courts of criminal jurisdiction to cater for the interests of vulnerable defendants, victims, and society, and to maintain the integrity of the legal process as one that is fair and just? The chapter evaluates the reform proposals of the English Law Commission and assesses how the law could be improved for all those who are involved in dealing with the unfit to plead.