The Ecosystem Service Assessment Support Tool (ESAST) has been designed to provide guidance to users who are new to ecosystem services and need assistance in designing an effective assessment process. It can also assist experienced users in providing detailed information about different concepts, methodologies and links to case study information, or give structured access to information maintained within and outside of Oppla (www.oppla.eu), an online platform where the latest thinking on ecosystem services, natural capital and nature-based solutions is brought together. The ESAST is divided into five main steps that can be carried out in an iterative fashion: (i) setting the scene; (ii) identification of ecosystem services; (iii) biophysical assessment; (iv) valuation; and (v) put into practice. Each step provides the user with the rationale, objective and the expected outcome of the step as well as resources, illustrative real-world cases, and tools and methods to be used in that stage of the assessment process. The tool can be accessed via Oppla and http://www.guidetoes.eu/.