This paper released by the National Legal Aid Defender Association in July 2015 responds to the growing use of actuarial risk assessments and needs assessments to make decisions about persons at various stages of the criminal justice system. As the use of these assessments increases, particularly in pretrial detention determinations, clients will benefit from defenders who understand the science behind assessments, can advocate effectively for their use, and know how to argue for fidelity of the risk assessment tool.