Prince Charles will officially open the Royal Welsh Show later, as the event celebrates its 100th year.
Prince Charles made a three-day tour of Wales last week
The show, which attracts more than 200,000 people over four days, was founded in Aberystwyth in 1904.
The Queen, the Royal Welsh Agricultural Society's patron, and Prince Philip, will be guests of honour on Wednesday.
First Minister Rhodri Morgan, Countryside Minister Carwyn Jones and Health Minister Jane Hutt will all attend the first day.
Prince Charles, who spent three days touring Wales last week, will visit stall-holders and exhibitors at the show, and will be shown several of the animals competing for prizes during the course of the week.
David Walters, chief executive of the Royal Welsh Agricultural Society (RWAS), said there would be many special attractions to enjoy.
"One of the highlights of the main ring programme will be a centenary cavalcade demonstrating 100 years of Welsh country life," he said.
"This will involve about 1,000 people and will take place on each of the four days."
There will also be an exhibition of paintings, drawings and sculpture by Welsh artists representing the past 100 years, which will tour Wales later in the year.
"I can assure everyone that the 2004 Royal Welsh Show will be an event not to be missed," added Mr Walters.
"As well as bringing our first 100 years to a successful close it will project us with renewed confidence into the next phase of our development as a leading force in Welsh agriculture."
Other attractions at the show include the King's Troop, who will be putting on their display of horsemanship,
There have been a record number of livestock entries this year, with 7,500 animals in 1,200 classes and special awards.
But it will not just be sheep, cattle and pigs who will be spotted at the Llanelwedd showground.
Two Asian water buffalo will also be making a debut appearance.
Visitors will also be able to see the new stone-built entrance to the showground which has been built over the last year to mark the show's centenary.
The Queen and the Duke last came to the show in 1983, and the Queen first visited as Princess Elizabeth when it was staged in Carmarthen in 1947.
After moving around the country for the first 60 years, the show settled at its permanent showground in Llanelwedd in 1963.
On Sunday, preparations for the show were hit by the news that Dr Emrys Evans, 80, chairman of the management board, had died.
Dr Evans was the current chair of the Royal Welsh Show Society and had served for many years on the Development Board for Rural Wales.