Monte Carlo
Physically Based Rendering: From Theory to Implementation
Comprehensive reference on physically based rendering techniques
Lecture 18: Monte Carlo Rendering (CMU 15-462/662)
An introduction to Monte Carlo ray tracing
Lecture 19: Variance Reduction (CMU 15-462/662)
An overview various variance reduction techniques for Monte Carlo rendering, covering bidirectional path tracing, Metropolis-Hastings algorithm, MIS, stratified Sampling, low-discrepancy sampling, blue noise, photon mapping, and finite element radiosity
The rendering equation
The classic Kajiya rendering equation paper introduced the "rendering equation" and the path tracing algorithm
Robust Monte Carlo Methods for Light Transport Simulation
the Academy Award-winning Ph.D. thesis by Eric Veach. It starts from bidirectional light transport algorithms and introduces multiple importance sampling and Metropolis light transport
Flavors of Sampling in Ray Tracing
An overview of different sampling strategies used in ray tracing.