This book provides an in-depth examination of the instrument of collaboration with justice, one of the more far-reaching investigative tools in criminal cases by which promises are made to otherwise unwilling 'offender witnesses' in order to persuade them to testify in the prosecution of others. In it a comparison is made between the law and practice of the Netherlands and that of several other jurisdictions – Germany, Italy and Canada – in which provision is made for the instrument. Drawing on legal and empirical research, this book offers a unique insight into the instrument by comparing the legal frameworks in place in each country, as well as the application in practice and challenges encountered in this context.