The 85-year-old announced the decision in Latin during a meeting of Vatican cardinals this morning.
He said that because of his age and diminishing strength, he didn't feel he could carry on.
On the Island, Lord Bishop Robert Paterson has described the Pope as having a formidable intellect but also formidably conservative.
He admits the resignation has come as a surprise:
Yellow weather warning for coastal overtopping
Strong winds are expected overnight
Plans approved for 'The Wing'
New billboard to be introduced at Ronaldsway Airport
Police appeal for video footage after 'significant' blaze
Site now deemed 'structurally unsafe'
Douglas to receive new lifeboat
Port St Mary is to lose one of its lifeboats in the next two years