Janez Potocnik, the European commissioner for the environment, said Green Week brings environmental experts together to call for a "radical change" in the approach to biodiversity.
"The world needs a reality check on the importance of biodiversity loss," he warned.
A key focus of the conference is to raise awareness about the potential business advantages of protecting biodiversity, the EU said.
More than 3,000 participants from across Europe are to take part in the 30 sessions during Green Week.
"This conference is an ideal forum for key players in the environment field to come together and pass a message about the need for a radical change in our approach to the crisis facing biodiversity," said Potocnik.
The conference runs through Friday.