Updated 1 June 2016
Spine Unity runtime classes are defined in the Spine and Spine.Unity namespaces.
In all C# code that you intend to refer to Spine classes, it will be useful to add using declarations on the top of the file:
using Spine;
using Spine.Unity;
// using Spine.Unity.Modules // if you are using modules
The Spine namespace contains all the shared base Spine classes implemented in C# (spine-csharp).
This includes Skeleton, Bone, Slot, Attachment, AnimationState, Animation, SkeletonJson. This represents Spine's core functionality like animation and file loading.
The Spine.Unity namespace contains Spine classes specific to Unity, including all components that handle rendering, Property Attributes and helper classes.
This includes SkeletonRenderer, SkeletonAnimation, SkeletonAnimator, and inspector property drawers [SpineAnimation], [SpineSlot], [SpineEvent], etc. It also includes the SkeletonExtensions extension methods for Spine C# classes.
The Spine.Unity.Modules namespace contains specialized optional/removable modules that may not be applicable to many users.
This includes Ragdoll, Ghost, SkeletonGraphic, SkeletonRenderSeparator, SpriteAttacher, YieldInstructions, 2D Toolkit support.
If you are using one of these modules, you need to add using Spine.Unity.Modules at the top of your C# code.
You normally don't need to interface with these classes but the Spine.Unity.MeshGeneration namespace contains certain implementations of mesh generation functionality. If you need to implement some specialized rendering code, the classes in this namespace can be useful.
