- Most simple and easy to understand discription is available in Rogers & Girolami's book "A first course in Machine Learning". Clicke here, to see screenshots of the chapters. Otherwise, I have a hard copy of the book which I am open to share.
- Bishop's "Pattern Recognition and Machine Learning" chapter 6.4, available online here.
Awesome introductory videos to avoid reading:
Inducing points approximation literature and Best Explanation video (talk) I have ever seen:
- Sparce Gaussian Process aproximations by Richard Turner on youtube.