in the whale-hunting debate
They say the mammals have become so abundant since a worldwide moratorium on commercial whaling that they are threatening stocks of fish, including cod.
But the decision was attacked by the UK and US Governments, as well as animal welfare groups.
The International Fund for Animal Welfare (IFAW) says there is no scientific basis for the operation, and that Iceland cannot use science to camouflage its desire to resume commercial whaling.
In Britain, the Royal Society for the Prevention of Cruelty to Animals is stopping short of calling for a boycott of Icelandic products, but it is asking consumers to think twice before buying fish from the island.
Iceland's own tourism industry has joined in the criticism, fearing that the decision could damage the country's image, and threaten the increasingly popular whale-watching business.
“Norwegians do it, Russians do it, Japanese do it, Americans do it, why can't we?”
Gisli Vikingsson - Marine scientist
"Whaling is part of Iceland's past, and must remain so,"
Greenpeace Executive Director Gerd Leipold said in a statement.
"While we don't expect to change everyone's minds, Greenpeace hopes that we are able to give many Icelanders the confidence to say no to whaling - forever."
Three ships were due to set sail from undisclosed locations over the coming days to avoid possible protests.
Iceland and the whale