Multiple CLIL writers (e.g. Ball, Kelly, & Clegg 2015) have emphasised the significant role of assessment in promoting learning in CLIL classrooms, where there is a dual focus on learning content and language (Genesee & Hamayan, 2016). Because of this dual focus, the assessment process in CLIL becomes more complex. Assessment in CLIL should provide insights into learner content and linguistic knowledge, as well as strategies used to learn both content and language in order to identify student progress and needs. This should inform both teachers and students in how to enhance learning. Despite excellent overviews, guidelines, and practical activities in CLIL assessment (Lin 2016; Mehisto & Ting 2017; Quartapelle 2012), teachers express concerns about adopting new assessment practices, principles, and techniques and are underusing the potential to support learning (deLuca & Bellara 2013; Hill 2017a; Tsagari & Vogt 2017).This chapter introduces (a) classroom-based assessment promoting learning, focusing on assessment for learning and learning-oriented assessment, (b) CLIL, and (c) teaching, learning, and assessment in CLIL. We will then synthesise these to inform our conceptualisation of assessment promoting teaching and learning of content and language in CLIL classrooms. A further role of this chapter is to introduce essential terms, notions, and conceptualisations used in the volume.We will next discuss classroom-based assessment promoting learning in general without discussing CLIL. Our intention is to set the boundaries of how we conceptualise