Heraclitus is the first reflective philosopher because he contemplated thinking itself. The Logos and its understanding are the essence of Heraclitus's philosophy. He aims for more than partial insights into areas we today refer to as metaphysics, epistemology, ontology, or philosophy of language; he seeks a comprehensive view of the world. This book addresses the many themes (critique of knowledge, thinking, cosmos, unity of opposites) that appear in the fragments of Heraclitus, but also their unity: If the Logos determines everything and thus everything is one, then a thinking and speaking that aligns with the perspective of the cosmic Logos is also a view of things that can grasp everything equally correctly and should guide both individual and communal practice. The reader is facilitated in understanding the philosophically oriented investigation, as the fragments are presented in a bilingual format and in detail.