The Númenóreans were descendants of the Edain of the First Age, who proved themselves allies of the Elves, from whom they gathered knowledge of all things surrounding them. The two races fought together against Morgoth.
During that Age, unions of Elves and Humans were made; Beren Erchamion and Lúthien Erchamion, whose son Dior Eluchíl, married Nimloth of Doriath and Elwing Azrubêl was born. Idril and Tuor, the second couple, were parents of Eärendil. Elwing and Eärendil met at the Havens of Sirion and from their union twins were born: Elros and Elrond. To the two half-elves, the Valar gave a choice: Elros chose to be mortal and join the humans, whereas Elrond chose to be immortal and join the elves.
When the last battle was won by the forces of Valinor, the Valar rewarded the Edain by giving them a place to dwell outside the troubled world of Middle-earth. Ulmo rose Elenna, later known as the Island of Númenor. Halfway between Endor and Aman, the descendants from the Three Houses established the Kingdom of Númenor in 32 2A and would last and dominate all other mortal peoples throughout the entire Second Age. Elros became the first King of Númenor.
The Númenóreans were extremely skilled in arts and craft, with the forging of weapons and armour; but the Númenóreans were not warmongers, hence the chief art on the island became that of shipbuilding and sea-craft. The Númenóreans became great mariners, exploring the world in all directions save for the westward, where the Ban of the Valar was in force. They often travelled to the shores of Middle-earth, teaching the men their art and craft, and introduced farming so as to improve their everyday lives. They also became skilled in the art of husbandry, breeding great horses that roamed across the open plains in Mittalmar. Although the Númenóreans were a peaceful people, their weapons, armor, and horse-riding skills could not be contested anywhere else in Arda, save for the Valar.
Before the Dúnedain, the Númenóreans learned the wisdom and were all given a great life-span by Eönwë, who came among the faithful Humans. The Númenóreans would live for more than 400 years. When they all reach their full maturity at the age of 50, they become ageless until they reach their final age.