Up to 20,000 people are expected to take part in the annual pilgrimage at Croagh Patrick today.
The event represents the busiest day of the year for Mayo Mountain Rescue, which has advised those taking part in the climb to come well prepared for cool weather conditions.
The tradition of climbing Croagh Patrick dates back more than 1500 years to the year 441, when St. Patrick fasted on the summit for 40 days and 40 nights.
Today pilgrims are expected to attempt the journey to the mountain's peak.
Mayo Mountain Rescue says it will be co-ordinating more than 150 volunteers who will be doing their best to ensure the day passes off as smoothly and as safely as possible.
More than 170 Order of Malta personnel will also be offering emergency medical assistance.
Those taking on the climb today are asked to come prepared for cool weather conditions, to bring suitable clothing, good footwear and plenty of water.