A large crowd, including visiting principals and ex Reivers and Reivers Lasses, was welcomed by festival committee president Ann Affleck.
She then invited last year's Reiver Scott Cullen and his Lass Susie Anderson to hand back their sashes of office.
Scott said: "It has been a great honour to be Reiver and I have been immensely proud to carry out my duties both in Duns and at other festivals throughout the Borders."
Susie thanked everyone for their support during her term of office and added "I have many great memories which will last for the rest of my life."
Mrs Affleck then announced the 2010 festival principals.
Reiver is 21-year-old Richard Burns, whose father Andrew was Reiver in 1984. Reiver's Lass is 21-year-old Ruth Drummond, daughter of festival chairman Ronald Drummond.
Their attendants will be 21-year-old Billy Walker, whose father was Reiver in 1957, and 23-year-old Morag Poole.
Mrs Affleck then presented Richard and Ruth with their sashes of office and presented all four with their official rosettes. Retiring Reiver's Lass Susie presented Ruth with a bouquet of flowers.
Richard said: "I will wear this sash with dignity and pride and hopefully uphold the standards set by those Reivers before me."
Ruth added: "I am thrilled to be Reivers Lass for 2010 and I will endeavour to uphold the good name of Duns throughout the Borders."
Mrs Affleck announced that the Reiver's colours this year will be Erin and Bishop.
This year's Wynsome Mayde O'Duns was also announced on Friday evening.
The honour of being Wynsome Mayde 2010 has fallen to April-Lea Taylor and her maids on honour will be Catherine Watson, Kelsey Renton, Rona Fleming and Ailie Herbert.
April was presented with a gift from the current Wynsome Mayde Kara White.
The Wynsome Mayde will be crowned during the festival week by Mrs Peggy Spouse MBE.