There have been considerable advances in welfare assessment in the past decades. This chapter explains some of the terminology related to welfare assessment and why the emphasis is moving towards including indicators of poultry welfare taken on the birds themselves rather than from the environment. It also reviews some of the more commonly used laying hen and broiler welfare assessment indicators, focusing on those that reflect the behaviour of birds. Among the clinical indicators discussed are assessments of pecking damage and bird cleanliness. Behaviour indicators include those that are recorded from undisturbed birds, such as vocalisation, and those that use a test situation. A welfare assessment protocol is a description of the procedures to collect the indicators. In the final sections of this chapter, methods to prioritise between different indicators, depending on the purpose of the assessment, and future trends to improve poultry welfare assessment are discussed.