This book is dedicated to the analysis of 49 of Euler's mathematical works, which he wrote between 1725 and 1741, i.e. during his life in St. Petersburg. The author describes Euler's mathematical production year by year. He starts with the work E1 and finishes with E790 (he refers to Euler’s individual works by their numbers in the Eneström index). At the beginning of each chapter he gives the full name of Euler's article in its original language and in English, the full quotation of the source (i.e. the name and pages in the original journals and in the Opera Omnia). Then he explains the mathematical content and adds a short list of literature. The topics of Euler's articles include series, geometry and curves, calculus of variations, elliptic integrals, differential equations, number theory, the theory of equations, topology and philosophy. The reader can find here some of Euler's important mathematical works, for example the Königsberg bridge problem, the Euler solution to the Basel problem, his first proof of the Euler-Fermat theorem, as well as his contributions to notation, calculus, etc. The book shows how Leonhard Euler grew from a young student of age 18 to a supreme mathematician and scientist of his time. The author creates a portrait of Euler and his mathematical production, which shows a connection with works of other mathematicians and its historical context. The book can be recommended to all people who are interested in mathematics and its history.