There are a few things you should know about merging edges: - Edges must be open. I recomend you to go to Display-Custom polygon options and check "Higlight Border edges" and put Border width value 3 or 4, so all open edges will be visible in 3D view. - edges must be part of the same polygon (use Polygon-Combine with objects selected) Sometimes edges can`t be merged even if all seems to be ok, I think it is a bug which is present since Maya 1.0. Sometimes restarting Maya will help, if not, delete the face that is aligned to the problematic edge and use Polygon-append to fill the hole. hope that helps