Speusippus: Article from the Stanford Encyclopedia of Philosophy by Russell Dancy. Reviews in depth what is known about his life and doctrines.
Speusippus: Brief entry from the 2001 Columbia Encyclopedia.
The Unwritten Doctrines: Plato's Answer to Speusippus: An essay by John Pepple, arguing that Plato's later works include a response to Speusippus' rejection of the Platonic forms.