Louis Éconches Feuillée (sometimes spelled Feuillet) (1660, Mane, Alpes-de-Haute-Provence – 18 April 1732) was a French member of the Order of the Minims, explorer, astronomer, geographer, and botanist.

He attracted the attention of members of the Academy of Sciences and in 1699 was sent by order of the king on a voyage to the Levant with Giovanni Domenico Cassini to determine the geographical positions of a number of seaports and other cities.

He returned to France in June 1706. his work won recognition from the Government, and he immediately began preparations for a more extended voyage along the western coast of South America to continue his observations.

He received the title of "Royal Mathematician" from Louis XIV of France, and armed with letters from the ministry, set sail from Marseilles on 14 December 1707.

He remained in that city for a month, conducting astronomic, botanical, and zoological surveys and at the end of February traveled to Valparaíso.

Between 1735 and 1744, scientists like Louis Godin, Charles Marie de La Condamine, and Pierre Bouguer would take part in similar expeditions.

Four months after Feuillée returned to France, Louis XIV dispatched the engineer Amédée-François Frézier to South America to report on Spanish fortifications there.

Frézier also disagreed with Feuillée in regard to the latter's measurement of the latitudes and longitudes of the South American coast and of the principal ports of Chile and Peru.

Upon his departure, with a hydrometer of his own invention, Feuillée showed the Mediterranean was saltier than the Atlantic, which proved its diffusion and advection (including their combination, convection currents) through the Strait of Gibraltar insufficient to cancel out their differing evaporation, precipitation and river discharge profiles.

He attributed the fact chiefly to the freshwater of the Amazon and other jungle rivers flowed far into the Atlantic, at a time when the complexities of the salinity of ocean water were little studied He drew a new map of South America.