From BlenderWiki

Papers and Resources

Various papers and resources, that may prove valuable.

PBRT

• Chapters 11 (Volume Scattering) and 16 (Volume Rendering).
• PBRT source code https://github.com/mmp/pbrt-v2 (BSD license)

Courses

• Production Volume Rendering Systems
• Volumetric Methods in Visual Effects

Papers

• Importance Sampling Techniques for Path Tracing in Participating Media
• Importance sampling of area lights in participating media
• Decoupled ray-marching of heterogeneous participating media

Various

• http://graphicsrunner.blogspot.de/search/label/Volume%20Rendering