As many as 300,000 people are expected at the National Ploughing Championships in Screggan near Tullamore this morning.
It is the 85th year of the event, the largest outdoor festival in Europe.
Traffic problems are expected as attendees descend on the rural area.
"We're asking in a big way for the co-operation of people this year and as normal, we're asking them to plan their route in advance and to do this, they can consult with Garda.ie or npa.ie for the traffic plan," said Garda Inspector John Lawless.
Around 1,500 exhibitors will be at the event, considered is the highlight of the farming year.
A new survey by Agriland has found that 70% of farmers do not make a regular wage from their business, and with the Budget only three weeks away, farmer are sure to have plenty to say to politicians making the trip to Offaly.
The gates open in Screggan at 9am, with the Ploughing itself starting at 10.30pm.