The last decade has seen a burgeoning of interest in the twin fields of school effectiveness and school improvement by politicians, policy makers and practitioners. For some, the drive has been to raise standards and increase accountability through inspection and assessment measures, believing that the incentive of accountability and market competition will lead to improvement. Alternatively, reform and restructuring have led many people in schools to create their own agenda and ask, 'How do we know that what we are doing makes a positive difference to our pupils?' and, 'What can we do to provide pupils with the best possible education?' This paper explores the two paradigms that underpin notions of school effectiveness and school improvement. We start with their definitions and aims. Key factors of effectiveness and improvement are examined and fundamental issues discussed. We conclude with a description of attempts to link the two areas of work.