This article examines the evolution of approaches to understanding tax obligation relation-ships. The author analyzes previously existing approaches to interpreting tax obligations, as well as their development. Based on significant changes in tax obligations associated with the transition to paying most taxes, fees, and insurance premiums to state extra-budgetary funds as a single tax payment, the author formulates a hypothesis regarding the existence of a single tax obligation. Based on an examination of its specific features and the stages of its fulfillment, the article provides a definition of a single tax obligation.