This paper explains the role of the police and criminal justice system in child protection in the U.K. It focuses on the immediate protection of children, the investigation and prosecution of crimes against them, and the prevention of abuse. The main responsibility for child protection in England is currently carried by Local Authority Social Services Departments. These work with other agencies - health, education and the police- to support families and investigate harm to children and care for children who cannot live with their families. The police (organized in 43 local forces across England) have powers to remove or detain children for their protection. Social services rely on this power for emergency intervention; the police also use it independently when they come across children who need immediate protection. Specialist police units, Child Protection Units, investigate crimes against children, generally working with social workers from the local authority. There has been some ambivalence in the use of the criminal law in child protection cases. Police have not always recognized that harming children is a crime and should be investigated as such. Social workers have been reluctant to involve the police because of concerns that this will discourage parents from being frank with them, put more strain on the family and prevent rehabilitation of children to their families. The substantive criminal law and the practice of the criminal courts have not served children well, and this has been recognized by the government. Various reforms have been undertaken and more are planned. Three types of police investigation are discussed seriousinjuries to young children, sexual offences and other crimes where children may be witnesses, and internet pornography The Crown Prosecution decides whether there should be a prosecution. The decision to prosecute and the conduct of trials with child witnesses are considered. The key issues relate to making it possible for children to give good evidence and preventing further harm to them in the process. The police also have a role in prevention of offences against children. Serious sexual offenders are required to register with the police and their whereabouts are monitored. Police records also provide the basis for ensuring that unsuitable people do not work with children. Hence prosecution has an important role for children other than thee immediate victims. Creating a criminal justice system that can be used to protect children demands substantial resources, particularly training for professionals at all levels, and systems for supporting children. The English experience provides an example of the many different things required. There remain difficulties in using the criminal law in child protection. However, not to use it gives a message that children can be harmed with impunity. It is not sufficient to change the law, community attitudes must also accept that children are harmed in their families and support action against people who harm children including parents.