A scene graph is a tree structure that tries to structure the objects in a scene accordingly to transformations, textures, materials and much more instead of just the geometrical representation of objects like for example a quadtree does. All games does contain a scene graph in some way, in the most simple form it could just be a root node and all other rendered objects as child nodes to the root node.

Here’s a list of useful links concerning scene graphs. Most links are borrowed from a post on gamedev.net but copied to this post so that I could remove broken links and include new ones.

• Wikipedia Entry for Scene Graphs
• Game Engine Architecture – Book Except (Scene Graphs)
• Understanding and Implementing Scene Graphs
• Scene graph & moving objects
• Terrain and scene graphs
• Scenegraph Management

• Scenegraphs: Past, Present and Future
• Game Object Structure: Scene Graphs
• Game Object Structure: Scene Graphs Revisited
• The GDC 2003 Game Object Structure Roundtable (scene graph section)
• Scene Graph/Renderer interface
• Scene Graph. DAG or Tree With Mesh List?
• Design Patterns used in the OpenSceneGraph
• API-agnostic vertex storage and conversion to API-usable storage
• Some UML class diagrams
• Nvidia implementation of a scene graph dedicated for good shader support

• SG integration
• Material/Shader implmentation
• Shader system implementation
• YASIT
• Shader Engine Design Decisions

• Optimized View Frustum Culling Algorithms for Bounding Boxes
• Optimized View Frustum Culling Algorithms
• Efficient View Frustum Culling

Most of this list was copied from the following gamedev.net forum thread.
http://www.gamedev.net/community/forums/topic.asp?topic_id=349829