Epistulae Morales ad Lucilium, or 'Moral Letters to Lucilius', is a collection of 124 letters written by the Roman philosopher Seneca to his friend Lucilius. These letters address various philosophical topics, providing insights into Stoic thought, ethics, and practical advice for living a virtuous life. The work illustrates Seneca's belief in the importance of moral philosophy and self-improvement as paths to a fulfilling life.