In Content and Language Integrated Learning (CLIL) programmes, non-linguistic content is taught and assessed in an additional language. Hence, CLIL teachers, most of whom are content subject specialists, may encounter difficulties in evaluating students' content knowledge independent of their L2 proficiency and in aligning objectives, instruction and assessment. These concerns are closely related to teachers' assessment literacy, which is seen as integral to teachers' pedagogical content knowledge and plays a crucial role in effective instruction and assessment. While frameworks for teachers' assessment literacy exist, there have been calls to re-examine this important construct with reference to specific disciplinary contexts. Given the curricular complexities of CLIL, this paper seeks to conceptualise the assessment literacy of teachers in such programmes. It will first tease out the complexities of assessment in CLIL programmes. It will then review some relevant literature on teachers' assessment literacy, based on which a conceptual framework for CLIL teachers' assessment literacy is proposed. It will also include an illustrative case of how the framework could be applied in research. The framework will establish a theoretical grounding for future empirical research in the field and have important implications for CLIL teacher education.