Salus populi suprema lex esto ( Latin: "The health (welfare, good, salvation, felicity) of the people should be the supreme law", "Let the good (or safety) of the people be the supreme (or highest) law",  or "The welfare of the people shall be the supreme law") is a maxim or principle found in Cicero's De Legibus (book III, part III, sub. VIII). 
The phrase is the state motto of Missouri, accepted, like many other states, as an element of its state seal. It also appears on many coats of arms, sometimes in variant forms such as Salus populi suprema lex, or Salus populi suprema est. These coats of arms include the City of Salford, the London Borough of Lewisham, Eastleigh, Harrow, Lytham St. Anne's, Tipton, Mid Sussex, West Lancashire, Swinton and Pendlebury, Urmston and Willenhall;  Manassas Park, Virginia, and the Duquesne University School of Law.
John Locke uses it as the epigraph in the form Salus populi suprema lex in his Second Treatise on Government and refers to it as a fundamental rule for government.  It was the inscription on the cornet of Roundhead and Leveller William Rainsborowe during the English Civil War. This motto was also endorsed by Hobbes at the beginning of Chapter 30 of Leviathan and by Spinoza in Chapter 19 of his Theological-Political Treatise. It was frequently quoted as Salus populi est suprema lex since at least 1737. 
- Cicero, De Legibus, Loeb Classics, p. 467.
- Cicero, Marcus Tullius. de Legibus. III. Free full text from the Latin Library. Retrieved on 2007-06-08.
- Mottoes in Latin
- Locke, John (1689). An Essay Concerning the True Original, Extent and End of Civil Government. Chapter XIII, section 158.
- Google Books search of books published before 1850
- The Dublin medical press. 16.