Objectives: Adapting health technology assessment (HTA) reports for different contexts could reduce the need for multiple reports on the same health technology with resultant saving of time and resources. This article describes an instrument, the adaptation toolkit, which has been developed to aid in the process of adaptation of HTA reports. Methods: The toolkit was developed by a partnership of HTA agencies and networks from across Europe. The role of the toolkit is to guide the user through the process of selecting possible relevant material from these report(s), assessing the relevance, reliability, and transferability of the material, and adapting it for the desired context. Results: The adaptation toolkit has been developed, it comprises a collection of resources that help the user assess whether data and information in existing HTA reports should and could be adapted for their own setting. The toolkit contains two sections: a preliminary speedy sifting section and the main toolkit. The main toolkit includes five domains: (i) technology use and development, (ii) safety, (iii) effectiveness (including efficacy), (iv) economic evaluation, and (v) organizational aspects. Legal, ethical, and social aspects are beyond the scope of the toolkit. The toolkit is designed for the adaptation of evidence synthesis rather than primary research. Conclusions: The completed current version of the toolkit contains checklists and resources to aid in the adaptation of HTA reports. This collection of resources is available for use by all HTA agencies and can be accessed at: http://www.eunethta. net/upload/WP5/EUnetHTA_HTA_Adaptation_Toolkit_October08.pdf..