This textbook is aimed at students who wish to enter the Economics Schools (Schools of the 5th Scientific Field) and was written to meet their needs in the subject "Principles of Economic Theory," which has increased importance and a coefficient of 1.3.

The purpose of the book is to help students understand all aspects of Economic Science included in the syllabus, so they can succeed with absolute success in the Panhellenic exams.

The student who has this book in their hands can delve into economic concepts, use the scientifically and systematically defined methodology for addressing economic problems, choose from a variety and multiplicity of applications, and tackle combinatorial and original questions in the new exercise models.

The book was written based on the principles of didactic and pedagogical science and the scientific completeness and rigor required by economic knowledge. Moreover, it reflects the experience and maturity of the authors in publishing school aids for over a decade.

The book includes topics that significantly upgrade the previous edition, which was an absolute success. We thank students and teachers for the trust and appreciation they have shown in our effort over the years.

Be assured that we have given our best for this book, we have given our soul!

We have worked passionately for Economic Science, we have raised the level of presentation of the syllabus, methodology, and exercises, we have imparted a different philosophy characterized by continuous deepening and renewal of economic knowledge.

(from the authors' preface)