This chapter describes the key tax law concepts and mechanisms that are frequently referred to throughout the analysis conducted in this book. It begins by briefly describing the general methodologies that need to be employed for the purposes of an income tax and a VAT analysis of cross‑border economic activities. It then examines the main concepts that are used for the purposes of the tax law analysis conducted in this book. For income tax purposes, the chapter examines permanent establishment and business profits, independent personal services, income from employment, royalties, technical services fees, income derived as an entertainer or a sportsperson and income from immovable property. For VAT purposes, the chapter examines place‑of‑supply rules, VAT registration of non‑resident suppliers and the reverse‑charge mechanism. While examining these concepts, the chapter also elucidates the general assumptions made by the author to conduct the tax law analysis of international sports events. The chapter concludes by providing an overview of income tax and VAT modalities of unlawful activities, predominantly from a domestic law perspective.