The 10th bi-annual Golden Oldies Rugby Festival is expected to attract over 900 players and spectators to Caernarfon over the next three days.
It is the first time Wales has played host to the festival and organisers anticipate it could give the local economy a £500,000 boost.
The aim is to provide the over 35s with an opportunity to play rugby.
Garin Jenkins, former Swansea, Wales and British Lion and Ynysybwl number 2 is Festival Ambassador.
Teams taking part include Wales, England, Scotland, Ireland, Lithuania, Switzerland, Germany, Spain, Russia, Israel, Italy, Romania, Portugal and Argentina.
Wales is represented by the GOGs (Geriatrics o Gymru) the only golden oldies rugby team in country which is based at Caernarfon Rugby Club.
"It is the first time Wales has welcomed the festival and we have 32 teams taking part, and we expect to welcome over 900 visitors to Caernarfon," said GOGs chairman, Emrys Jones.
He added the Golden Oldies rugby provides a great opportunity for the over 35s of both sexes to keep fit and enjoy physical exercise in a "sporting and lighted manner".
As part of the festival the town's rugby club is hosting a rugby tournament on Saturday.
The Welsh Assembly Government is backing the event and Minister for Heritage, Alun Ffred Jones, said he was delighted the festival was in north Wales.
"Caernarfon provides a stunning backdrop for what promises to be a fun filled feast of rugby," he said.
"I'm sure many of the competitors will be visiting Caernarfon for the firs time so I hope everyone will enjoy their time here," he added.
The opening ceremony will be held in Caernarfon castle.
Head custodian Tristian Jones said it was great for the town.
"We look forward to welcoming our European friends here so they can discover more about Caernarfon and Wales' heritage," he said.
The festival will take place from 10 -13 June with the opening ceremony at Caernarfon Castle at 1930 BST on Thursday evening.
The first game will be played on Y Morfa at Caernarfon Rugby Club at 1000 BST on Friday morning when the GOGs take on an Italian team.