Columbia Encyclopedia: Santayana, George: Life, philosophy, and bibliography.
George Santayana Themes and Sites: Links to a wide range of resources about Santayana and quotations from his works organized by recurring themes in his philosophy, by T.P. Davis.
Jorge Agustín Nicolás de Santayana: Article and bibliography at the Books and Writers website.
MSN Learning & Research: Santayana, George: Short biography.
Stanford University - George Santayana: Entry in the Stanford Encyclopedia by Herman Saatkamp.
The Critical Edition of Works by George Santayana: Collecting and publishing a critical edition of the works, edited by Herman J. Saatkamp Jr.
The Letters of George Santayana Book One: Michael Hodges reviews this book together with the fith volume of The Works of George Santayana. From Notre Dame Philosophical Reviews.
University of Waterloo - Overheard in Seville: Bulletin of the Santayana Society: Journal dedicated to the study of Santayana's life and work. Includes tables of contents, PDF files of many articles.