De l’Esprit des Loix. Ou du rapport que les Loix doivent avoir avec la Constitution de chaque Gouvernement, les Moeurs, le Climat, la Religion, Le Commerce, &c. à quoi l’Auteur a ajouté Des recherches nouvelles sur les Loix Romaines touchant les Successions, sur les Loix Françoises, & sur les Loix Féodales. Tome Premier [Tome Seconde]
Geneve, chez Barrillot & Fils 
2 volumes, quarto, 24.0 x 19.0 cm, very fine contemporary quarter pale continental, possibly Danish, calf and marbled boards, spines richly gilt, contemporary pale morocco labels lettered gilt, pp.(8), xxiv, 522; (4), xvi, 564, with the half titles to both volumes, printers woodcut to titles, with the cancels E3, F3, F4, Aa, Ff2, Kk2, Sss4 in volume I and a, Hhh in volume II, contemporary ownership in ink on front blanks W.E.Suedelius, an exceptionally fine, near immaculate copy of the true first edition.
Printing & the Mind of Man 197. En Français dans le Texte 138. Kress 4920. Goldsmiths 8375. Tchemerzine,VIII,459 (a).
See Volpilhac-Auger, G.Sabbagh & Weil: Un auteur en quête d’êditeurs? Histoire éditoriale de l’oeuvre de Montesquieu. 2011, pp.47-67, 413-416. It is believed that the first edition was printed in 500 t0 1500 copies, nobody really knows; part of the edition seems to have been seized by customs or lost in transport; in particular a large number of copies sent to England seem to have disappeared. Montesquieu was horrified by the errors he found which explains why no less than four kinds of errata were printed from January 1749 - three of which were destined for the first edition and inserted in the last copies that had been unsold and uncirculated by that time.
FIRST EDITION of Montesquieu’s [1689-1755] great L’esprit des loix in which he argued that the best government would be one in which power was balanced among three groups of officials. He thought England - which divided power between the king (who enforced laws), Parliament (which made laws), and the judges of the English courts (who interpreted laws) - was a good model of this. Montesquieu called the idea of dividing government power into three branches the "separation of powers." He thought it most important to create separate branches of government with equal but different powers. That way, the government would avoid placing too much power with one individual or group of individuals. He wrote, "When the [law making] and [law enforcement] powers are united in the same person... there can be no liberty." According to Montesquieu, each branch of government could limit the power of the other two branches. Therefore, no branch of the government could threaten the freedom of the people. His ideas about separation of powers became the basis for the United States Constitution.
John Maynard Keynes in the manuscript preface to his French edition of The General Theory described Montesquieu as the greatest French economist: “Montesquieu was the real French equivalent of Adam Smith. The greatest of your economists, head and shoulders above the Physiocrats in penetration, clear-headedness and good sense”.