Governments and other stakeholders have become increasingly interested in assessing the skills of their adult populations in order to examine how well prepared they are to meet the challenges of the modern knowledge-based society. The current paper provides a conceptual framework for the assessment of reading component skills in the OECD’s Programme for the International Assessment of Adult Competencies (PIAAC). The assessment of component skills is intended to provide a greater level of information about the skills of individuals with low levels of literacy proficiency than has been available from previous international assessments. The ‘component skills ’identified for the assessment are vocabulary knowledge, sentence processing and passage comprehension.