When Seneca the Younger turned his back on politics, having previously advised the increasingly volatile Emperor Nero, he became one of Rome's most prolific authors and spent his retirement writing about Stoic philosophy. The most intriguing output of that time are Seneca's Epistulae Morales, a collection of letters on ethics that is addressed to his friend Lucilius. In these letters, Seneca writes about his everyday struggle to be a good person and to live according to the principles of Stoicism, while helping his friend embark on his own philosophical journey. This book is the first modern commentary in any language on the second book of Seneca's Epistulae Morales in a modern language. It includes an edition and translation of the text as well as a substantial introduction. The aim of the commentary is to make the text more accessible to modern readers through a detailed linguistic, philosophical, and literary exegesis of the letters. The commentary lays great emphasis on showing that the book unit plays an important role in the larger epistolary corpus and argues that the book composition is essential for our understanding of ancient letter writing. The commentary demonstrates that the letters are connected to each other by an intricate web of references, repeating, developing, and deepening ideas throughout the letter exchange.