The Programme for International Student Assessment (PISA) is an international study coordinated by governments of participating countries, through the Organisation for Economic Co-operation and Development (OECD). In 2000, a total of 265,000 students from 32 countries took part in PISA. The main aim of PISA is to assess how well 15-year-old students are prepared to meet the challenges of today's and tomorrow's knowledge societies. The assessment is forward looking, focusing on young people's ability to use their knowledge and skills to meet real-life challenges, rather than mastering a specific school curriculum. Assessing young people at the end of their compulsory education is regarded as providing valuable insights into the performance of basic education systems (OECD, 1999, 2001). In this Special Issue, the rich data collected in the OECD PISA 2000 study will be exploited in various secondary analyses. These analyses mainly focus on socio-economic and cultural factors related to or associated with learning outcomes in reading and science. Some articles compare educational systems and cultures in all the Nordic countries, while others focus on two or only one of the countries. The authors of the articles in this issue work as researchers in the national PISA teams of the Nordic countries, which all take part in the PISA programme.