This book provides an English translation of the early fundamental contributions of Lothar Meyer (1830-1895) regarding his independent discovery, coincident with that of Dmitrii Mendeleev, of the periodic system of the elements. Although an English translation of the 5th edition of Meyer´s book Modern Theories of Chemistry and their Significance for Chemical Statics was published in 1888, this will be the first time that these crucial early texts will be available in English. These writings reveal details regarding Meyer´s research pathway to the idea of periodicity and to an arrangement of the chemical elements in tables and graphs. An introductory commentary and interpolated editorial footnotes to the texts clarify the (physico)-chemical background regarding the various shifts in thought during the crucial period from 1860 to the early 1870s. A short biography of Lothar Meyer completes the book. The volume includes a complete translation of the first edition of Modern Theories of Chemistry and their Significance for Chemical Statics (1864), the ground-breaking paper “The Nature of the Chemical Elements as a Function of their Atomic Weights” in Annalen der Chemie und Pharmacie, suppl. vol. 7 (1870), 354-64, and portions of the revised second edition of Modern Theories of Chemistry and their Significance for Chemical Statics (1872).