The Australian Education Research Organisation (AERO) has created the first longitudinally linked dataset of Australian students' National Assessment Program -- Literacy and Numeracy (NAPLAN) participation and results. This technical paper describes the creation of the Longitudinal Literacy and Numeracy in Australia (LLANIA) dataset, including the linkage process and quality assurance methods. The final linked dataset comprises data from 6,270,515 students who were enrolled in the Australian education system from 2008 to 2021. Around 25% (n = 1,594,261) have fully linked data from Year 3 to Year 9. This includes fully matched records for 81% to 86% of students in Year 3 in 2009 to 2013 and 2015 (N = 1,654,716) who completed all 4 rounds of NAPLAN testing. The LLANIA dataset is expected to support a wide range of future projects, contributing to new knowledge both within theoretical and applied contexts. This dataset provides the ability to track students' performance and growth throughout their schooling and assess the effectiveness of learning interventions, creating significant potential for using empirical evidence to support Australian education policy and practice.