Westron was the native language at the time of the War of the Ring of all those Men and Hobbits living in the old areas of Gondor and Arnor, and also of those inhabitants of the west bank of the River Anduin as far north as the Gladden Fields, with the exception of the Woses, the Dunlendings, and the Rohirrim.

In addition, Westron was the common tongue for all interlingual meetings, and as such was known to some degree by everybody west of Rhûn. Westron was also the public language of the Dwarves and the base for many Orkish tongues.

Westron was in origin a mingling of Adûnaic and the languages of the coastlands of Middle-earth, developing in the third millenium of the Second Age with the establishment of Númenorean settlements in Middle-earth.

With the coming of Elendil to Middle-earth, the language was enriched with many Sindarin words, and this was the form in which Westron spread through Middle-earth.

There are very few examples of genuine Westron given in The Lord of the Rings, as most Westron names have been translated into equivalent English forms.
Encyclopedia entry originally written by tarkena