Principal Voices is a project aimed at stimulating discussion on some of the major issues facing our world today.

Throughout 2006, TIME, FORTUNE and CNN, in association with Shell, will be bringing together a group of globally-renowned experts - Principal Voices - in a series of videos, articles and round-table discussions.

The themes covered will be Urbanization, the Environment, the Collaborative Corporation and Economic Development. The Principal Voices will explore some of the key issues involved in these areas, and offer their ideas and opinions on how to meet the challenges facing the planet as we move forward though the 21st Century.

In 2005, a separate group of Principal Voices discussed the environment, business, the economy and transport. Click here to read full coverage of Principal Voices 2005, including the White Papers, transcripts of the debates and readers' comments.