This book, Volume I, was specifically written for the Panhellenic Written Competition 2G/2022/ and is a fundamental and essential aid on the subject of Macroeconomic aggregates. The reader can conceptually delve into the economic phenomena of GDP, economic growth, the SOLOW model, the Cobb-Douglas model, etc. Additionally, the multiple-choice questions aim at the complete understanding of these economic phenomena. The structure of the book, the writing style, and the development of the topics enhance the rapid reading and understanding of the material by the reader. Specifically, the book includes: Complete theory of Macroeconomic concepts in extensive analysis Simple diagrammatic analyses and examples for easy understanding Published examples and diagrams from distinguished EU sources Competition topics from previous years 225 multiple-choice questions with relevant suggestions after each subsection of the material to ensure immediate comprehension of the concepts and potential topics by the reader. Volume 1 covers the following topics of section 8 Macroeconomic Aggregates and National Accounts: 8.1 Gross Domestic Product, 8.2 GDP per capita, 8.3 GDP Economic Growth Rate, 8.4 Causes of GDP increase and production factors, and 8.5 Gross National Income.