An Imperial Wedding was what happened when an Emperor of Barrayar got married.
- "The most recent wedding of a ruling emperor had been the scrambling mid-war union of Gregor's grandfather Emperor Ezar to the sister of the soon-to-be-late Mad Emperor Yuri, which for a number of sound historical and aesthetic reasons Alys was loath to take as a model. Most other emperors had been safely married for years before they landed on the throne. Prior to Ezar one had to go back almost two hundred years, to the marriage of Vlad Vorbarra le Savante and Lady Vorlightly, in the most gaudily archaic period of the Time of Isolation."
- ―Imperial Weddings[src]
As a result, when Emperor Gregor Vorbarra and Laisa Toscane decided to marry, it was necessary to dust off a great many ancient protocols and decide which to keep, which to jettison, and which to modify to reflect more modern sensibilities. For example, the get-married-in-the-nude protocol was modified so that each of them got a brief physical exam shortly before the event in the presence of members of the opposite family, who then publicly declared their satisfaction with the non-mutie-ness of the spouse.
The two of them ended up with an official betrothal during Winterfair and two weddings; one as the heart of the Midsummer festival on Barrayar and a second on Komarr. The Midsummer event is described in some detail in the epilogue to A Civil Campaign.