The literature across different fields defines ageism ambiguously and widely covers a span of intolerant knowledge, values, attitudes and behaviors towards older adults or more generally toward people of a certain age. In this chapter we provide an overview of how ageism is defined, measured, and assessed in health care and long-term care. In so doing, we aim to bridge the gap between the concept and measurement of ageism in these two contexts and to provide some general insights into the approaches, which researchers can apply to assess ageism in these settings. In this chapter, we therefore aim to answer the following questions namely (i) Why is it important to know how ageism in healthcare and long-term care has been empirically studied? (ii) What evidence for the existence of ageism among key stakeholders (e.g. health care professionals and long-term care workers, family members and older adults) is reported in empirical research covering these two contexts? and (iii) Which are the conceptual and methodological approaches used to measure and assess ageism involving these key stakeholders in the two contexts?