The existence of these little—known elementary proofs convinced me that a naive approach to Lie theory is possible and desirable． The aim of this book is to carry it outdeveloping the central concepts and results of Lie theory by the simplest possible methods， mainly from single—variable calculus and linear algebra． Familiarity with elementary group theory is also desirable， but I provide a crash course on the basics of group theory in Sections 2．1 and 2．2．