In this Element, I first introduce intelligence in terms of historical definitions. I show that intelligence, as conceived even by the originators of the first intelligence tests, Alfred Binet and David Wechsler, is a much broader construct than just scores on narrow tests of intelligence and their proxies. I then review the major approaches to understanding intelligence and its development: the psychometric (test-based), cognitive and neurocognitive (intelligence as a set of brain-based cognitive representations and processes), systems, cultural, and developmental. These approaches, taken together, present a much more complex portrait of intelligence and its development than the one that would be ascertained just from scores on intelligence tests. Finally, I draw some take-away conclusions.