Gottlob Frege is celebrated for his distinction between the Sinn and Bedeutung – the sense and reference – of a term. The distinction is readily understood. The reference of the name ‘Plato’ is the bearer of the name, that most famous and widely revered philosopher, who lived more than two thousand years ago in ancient Greece. The sense of the name ‘Plato’, on the other hand, corresponds to what we would ordinarily recognize as belonging to its meaning: what speakers and hearers understand by the word that enables them to identify what they are talking about and to use the word intelligently. Why is Frege celebrated for this distinction? After all, just a generation or two before, Mill (1843) expounded his distinction between the connotation and denotation of a name. In The Port Royal Logic, Arnauld (1662) drew a kindred distinction between an idea and its extension. In his Summa Logicae, William of Ockham (c. 1323) distinguished between the term in mental language associated with a word and what it supposits. Earlier still, in ancient times, the Stoic logicians distinguished between an utterance, its signification, and the name-bearer. This is a very natural distinction, and we find variations on its theme reappearing throughout philosophical history. What makes Frege's distinction so noteworthy? The answer lies with his compositionality principles, one for reference and the other for sense.