The analysis offered here is based predominately on the lectures of Ferdinand de Saussure. Many of the ideas have been modified in an attempt to place them within the contemporary framework. For an unfiltered version of this story, check out the text itself:
Course in General Linguistics: Ferdinand de Saussure. 1972. Open Court Publishing Company. LaSalle, Illinois. (Translated by: Roy Harris).
Don't let the date fool you, though. The text is actually a compilation of lecture notes taken by his students around the turn of the century. If you're feeling particularly ambitious, it was originally published in Saussure's native French.