Problems with the current methods of attaching child restraints to the vehicle structure have led to the development of new attachment systems. These proposals have been coordinated by the International Standards Organization (ISO) with the intention of generating an international standard system for the attachment of child restraints--ISOFix. These proposals attempt to balance the requirements for good impact performance with ease of use, low misuse, and reasonable cost, against possible complexity of the child restraint and its installation into the vehicle. This research program investigated the use of a range of four different prototype systems by parents. These systems were also subjected to frontal, side, and rear impacts. Various degrees of slack were introduced into the systems to determine the sensitivity to misuse and its effect on impact performance. A conventional child restraint using the same child seat shell was used for comparison. The results demonstrated that all systems could perform well, particularly in the frontal impact tests, provided that any adjustment in the attachment system was tightened. However, some systems were particularly sensitive to slack. Overall, those systems with rigid attachments performed best, particularly in side impacts. Also these were favored by the user group.