This document provides guidance on the assurance of services when there are safety implications associated with the use of those services. These services we call “safety-related services”; typical examples might be an ambulance dispatch service or an air traffic control service.This guidance is aimed at services that are genuinely safety-related. Excluded services, which are considered critical, but not safety-related, include banking services or public broadcasting.A set of principles for assuring services (as opposed to systems) is proposed. The guidance explains how they may be applied in a service provision situation. These principles are domain agnostic and can be used across a wide range of service scenarios in diverse sectors.Further guidance is provided on how to apply the principles through objectives and how to address the challenges that may be encountered.Methods and techniques applicable to service situations are covered. Analyses are listed for identifying undesired behaviour where assurance is required.Of particular significance is how to show that the intent of the service assurance requirements is maintained through the service definition, service architecture and the agreements made at service interfaces (e.g. Service Level Agreements (SLAs)) and that the principles are preserved through change.The approach described in this guidance draws upon concepts from modular assurance and illustrates the different types of “wrapper” that can be used to manage the variety of assurance positions presented by services: these can vary widely in nature as the confidence in the assurance of intended behaviour can be difficult to establish.The principles are linked to objectives and characteristics to show how high-level requirements can be established for assured services.