Gaussian Processes for Machine Learning, Carl Edward Rasmussen and Christopher K. I. Williams, 2006 (The MIT Press)DOI: 10.7551/mitpress/3268.001.0001 - A primary textbook on Gaussian Processes, thoroughly detailing classification, latent function models, Laplace approximation, and Expectation Propagation.
A family of algorithms for approximate Bayesian inference, Thomas Peter Minka, 2001Ph.D. dissertation, Massachusetts Institute of Technology (Massachusetts Institute of Technology) - Introduces Expectation Propagation (EP) as an iterative method for approximate Bayesian inference, particularly applicable to GP classification.