SO/IEC 27041:2015 provides guidance on mechanisms for ensuring that methods and processes used in the investigation of information security incidents are "fit for purpose". It encapsulates best practice on defining requirements, describing methods, and providing evidence that implementations of methods can be shown to satisfy requirements. It includes consideration of how vendor and third-party testing can be used to assist this assurance process. This document aims to - provide guidance on the capture and analysis of functional and non-functional requirements relating to an Information Security (IS) incident investigation, - give guidance on the use of validation as a means of assuring suitability of processes involved in the investigation, - provide guidance on assessing the levels of validation required and the evidence required from a validation exercise, - give guidance on how external testing and documentation can be incorporated in the validation process.