Human languages are strikingly different from each other, and also strikingly the same. One of the most indecipherable codes used in World War II was Navajos speaking their native language. Yet the Navajos were able to translate messages to and from English quickly and accurately. This shows that, for all their differences, languages must have a strong common denominator. Linguistic research is discovering that, in spite of the differences among human languages, the underlying rules that form them are virtually identical. Just as a small number of discrete elements (atoms) combine to form all physical substances, so a small number of discrete factors combine to form languages as varied as English, Japanese, Mohawk, and Hixkaryana. All sentences in all languages are built following a common recipe, called Universal Grammar. That recipe contains a finite number of choice points, called parameters, which interact with each other in complex ways. As a result, the shapes of phrases and sentences in languages look completely different, even though the underlying rules that form them are almost identical.