Maven mirrors/respoitory question

Greetings,

I have a local maven repository that contains versions of my project's 
dependencies that are different than those provided by the upstream 
repository on the Internet. Currently some maven commands are failing for 
me because they are trying to download a version of the dependency that is 
not available upstream. How can I configure maven to look at my local 
repository first and if it doesn't find what it is looking for there fall 
back to the Internet repository.

Best,
Jack