Goods and services tax (‘GST’) is one of Australia’s most important and widely encountered taxes. According to the 2023 Budget Papers, GST is expected to raise approximately $88,042 billion in 2022/23, making it the second largest tax behind income tax. GST revenue is paid by the Commonwealth to the states and territories under special revenue-sharing arrangements. GST is a broad-based transactions tax which, like the value added tax (‘VAT’) that operates in many jurisdictions overseas, generally applies at each stage of the supply chain. The way it basically works is that registered entities charge GST on their supplies (ie outputs) and are entitled to credits for GST charged on their acquisitions (ie inputs). The burden of GST is designed to ultimately fall on end consumers who are not registered and are therefore not entitled to any credits for GST charged on the things they acquire. This chapter outlines the background to the introduction of GST and explains the basic principles that underpin its operation. The chapter focuses on the concepts of ‘taxable supplies’ and ‘creditable acquisitions’, which are the core building blocks of the GST system.