PISA (Programme for International Student Assessment) is designed to assess the scientific, mathematical, and reading literacy skills of 15-year-olds. It is a project of the Organisation for Economic Co-operation and Development (OECD). First conducted in 2000, PISA runs in three yearly cycles. This guide focuses on how Irish students performed on science in PISA 2006, compared to students in other countries. The target audience for the guide is teachers of science in postprimary schools in Ireland. Several reports on PISA 2006 have already been published. Readers who would like more information on PISA 2006 than is presented here are referred to the relevant Irish (Eivers, Shiel & Cunningham, 2007, 2008) and OECD reports (OECD, 2007b). This guide is divided into seven chapters. Chapter 1 provides some background to PISA and explains how scientific literacy was assessed. Chapter 2 compares the performance of Irish students on science to the OECD average and to the performance of students in other countries. Chapter 3 provides examples of PISA science items, and describes the types of response provided by students. Chapter 4 compares science as conceptualised in PISA and the Junior Certificate science syllabus, and Chapter 5 describes students’ science-related attitudes. Chapter 6 examines factors relating to test performance. Finally, Chapter 7 summarises the findings and presents some conclusions.