In three hours the International Court of Justice will make a ruling on the legality of Japanese whaling in the Southern Ocean.
Conservation groups hope Australia and New Zealand will win in their case and that whaling in the Southern Hemisphere will be stopped forever.
The issue has led to numerous battles at sea.
"We're hopeful for a clear verdict and one that doesn't further complicate what has been a complex political situation for more than two decades now," says the International Fund for Animal Welfare's Patrick Ramage.
Japan allocates itself an annual quota of around 1000 whales in Antarctic waters. It says it kills them for "scientific research", which is exempt from an international whaling moratorium.
The whale meat is then sold at high prices in Japan.
"It's not science. It's whaling for commercial purposes," says Mr Ramage.
The case against Japan's whaling was brought to the court by Australia, with contribution from New Zealand.
"The case was very well argued by the Attorney-General but it's a long away from a slam dunk that goes our way," says Prime Minister John Key.
Those following the case closely say it is almost impossible to know which way tonight's ruling will go and it is highly likely to be nuanced rather than clear-cut.
But it could be the final blow to Japan's operations in the Southern Ocean.
"The chances are quite remote that Japan would blithely ignore a judgement made by the International Court of Justice," says Mr Ramage.
Conservationists say even if tonight's ruling does mark the end of whaling in the Southern Hemisphere, the fight will go on to save those still being slaughtered in the north.