Drawing on in-depth interviews with prosecution witnesses subject to very serious and, in some cases, life threatening intimidation, the authors examined the nature of the intimidation the witnesses suffered and its impact on their lives. In cases in which witnesses and their families were permanently relocated away from their home areas by one of a growing number of witness protection programs run by the police, the authors considered the difficulties faced by these witnesses in rebuilding their lives in new communities. Of 142 witnesses identified, 55 were assessed as Level I witnesses, defined as being at high or very high risk of life threatening intimidation. For those 55 witnesses, information was recorded on a range of variables, including type of crime witnessed, nature of the threat against them, and whether the threat had been realized. The witnesses were found to have experienced a wide range of intimidation. This often took the form of verbal abuse and threats to life and property. The police witness protection program was established to arrange the permanent and secret relocation of witnesses and their families to a place where they could begin a new life. Experiences of witnesses in new communities demonstrated their concerns and anxieties were similar to experiences of protected witnesses elsewhere. While relieved to have found a place of safety, witnesses faced considerable social and psychological challenges without the immediate support of family and friends. 35 references, 5 footnotes, and 1 table