The Prime Minister David Cameron, Alex Salmond and the Princess Royal are set to join thousands of visitors at the sixth annual Armed Forces Day.
Crowds will enjoy piping, parades and a display by the world-famous Red Arrows as Britain marks the contribution of servicemen and women past and present in Stirling, Scotland.
There will be entertainment in the form of a parachute display and displays by Typhoon and Tornado jets, with Stirling Castle providing the backdrop.
Armed Forces Day was established in 2009 to honour the country's servicemen and women and their families across the Army, Navy and RAF.
This year's event will see tanks and military vehicles on display and demonstrations by Sea King, Apache and Puma helicopters. Plane enthusiasts will get the chance to see the Lancaster, Spitfire and Hurricane in flight.
The estimated cost of hosting the event is about £524,000, but organisers suggest it will earn about £1 million for the local economy as well as boost Stirling's profile as a tourist destination.
Both David Cameron and First Minister Alex Salmond will attend along with other senior politicians from Westminster and Holyrood, and the Princess Royal.
Poppyscotland chief executive Ian McGregor said: "Poppyscotland, together with our parent charity The Royal British Legion, are delighted to support the Armed Forces Day National Event in 2014.
"As Stirling is the host city, the event gives us an excellent opportunity to highlight both the wide range of vital support provided by Poppyscotland to those in the Armed Forces community living north of the border, and the complementary services of The Royal British Legion throughout the rest of the UK."
Meanwhile, Saracens rugby stars made a surprise visit to Camp Bastion, Afghanistan, to mark Armed Forces Day.
They were shown techniques used by the Force Protection group to defend the camp and surrounding air routes, while the sportsmen held a coaching session for troops.
Members of 15 Squadron, RAF Regiment returned the favour by putting the Saracens players through their paces with challenges such as evacuating a casualty from a watch tower and carrying a stretcher to safety under simulated attack.
Flanker Will Fraser said: "That was hard work. Not only is the stretcher hard to run with but the other kit, such as the helmet and body armour, adds to the difficulty. I have total respect for the service personnel here who have done this for real with their wounded colleagues on a stretcher."
Flight Lieutenant Damien Handley, 15 Sqn Operations Officer, added: "It's rewarding when you see professional athletes doing the same thing that we do and having to work hard at it. It makes us feel appreciated for the hard work that we do."
Those wanting to mark the occasion today can adopt a "Twibbon" which will add an image of the Armed Forces on their Twitter or Facebook profile.
The annual celebration is being held in Scotland for a second time, on the same weekend Stirling marks the 700th anniversary of the Battle of Bannockburn.
The two-day Bannockburn Live event will feature a re-enactment of the legendary clash which saw Robert the Bruce defeat the English army led by Edward II in 1314.
Despite the events being held so close to one another the potential for them to be used by independence and unionist supporters as the countdown to September's referendum continues has been dismissed.
Launching the programme for Bannockburn Live last month, Scotland's Tourism Minister Fergus Ewing said "it will be a weekend where we put politics aside".
More than 300 ''warriors'' will perform on the Bannockburn battlefield in scenes choreographed by the team behind the battle sequences in hit films Gladiator and Robin Hood, and visitors will have the chance to trace their ancestral roots and experience life as it was lived in the 14th century.
The festivities began last night with Pipefest, when pipe bands, Scottish clans and highland dancers joined a parade from the gates of Stirling Castle through the city.
VisitScotland chairman Mike Cantlay said: "The teams for Pipefest, Armed Forces Day and Bannockburn Live are working hard to ensure Stirling's Big Weekend is one to remember.
"Never before has this stunning city hosted as many tourists from all over the world and it really is Stirling's time to shine, showcasing the attractions, landscapes and history of this amazing area."
The National Trust for Scotland and Historic Scotland have been working for months to transform the Bannockburn site ahead of the 700th anniversary celebrations.
Historic monuments have been restored and a new visitor centre has welcomed thousands of visitors since opening earlier this year.