Quote Originally Posted by MacMillan of Rathdown View Post

Medals are appropriately worn with civilian black tie (PC or tuxedo) when the host of the event makes it clear that the wearing of medals is appropriate. The invitation, or admission ticket to the event will clearly state "Black Tie, decorations". If the invitation does not mention decorations then no medals should be worn.
Unless it is a military type event, in which case the wear of medals is always appropriate, whether mentioned or not, like the military ball he mentioned.