What's the difference between shivering and shuddering?

Hello,
What's the difference between shivering and shuddering?
They just seem to have the same meaning. Is there a concise difference?

You are right in believing that they have very similar meanings. Both 'shivering' and 'shuddering' refer to small movements back and forth. They are used in different situations, though. When applied to human beings, 'shivering' almost always means the physical reaction caused by cold. 'Shuddering' is usually reserved for the shaking caused by a strong emotion like fear, horror, or revulsion.

yes Gjones2 is I think right, I also seem to think "shuddering" is a much more violent shaking of one's self than "shivering".

I agree with Frances - shuddering is a much more physical effect - it also affects non-animal objects. Aircraft experience shuddering during turbulence - never shivering!