The interaction between taxpayers and the Public Administration begins with the existence of a triggering event. Hugo de Brito Machado (2013) states that when a law describes an event capable of creating a link between an individual and the State, the event outlined in the law becomes the triggering event that gives rise to the tax relationship. From this point, two scenarios emerge: the taxpayer must act within the legal framework governing the triggering event and its implications, while the State must ensure the provision of necessary information for the taxpayer to fulfill their obligations and verify compliance with legal requirements. In a context of increasing complexity in tax legislation and the pursuit of fiscal justice, this study aims to clarify the fine line between lawful and unlawful tax practices, specifically addressing Tax Avoidance (Elisão), Evasion (Evasão), and Aggressive Tax Avoidance (Elusão). To achieve this, we will examine the legal and jurisprudential foundations of these concepts.