What are the five biggest global challenges we face right now — and what can we do about them? This hour, TED speakers explore some radical solutions to these enduring problems. Guests include geoengineer Tim Kruger, president of the International Rescue Committee David Miliband, political scientist Ian Bremmer, global data analyst Sarah Menker, and historian Rutger Bregman.

Our approach to treating disease is, in many ways, narrow and rooted in the past. Is it time for a new paradigm? This hour, TED speakers share their visions for new ways to understand medicine. Guests include cancer physician and writer Siddhartha Mukherjee, surgeon and writer Atul Gawande, neurosurgeon Jocelyne Bloch, and internist Joseph Ravenell.

Are deception and secrecy categorically wrong? Or can they be a necessary means to an end? This hour, TED speakers share stories of going undercover to explore unknown territory, and find the truth. Guests include poet and activist Theo E.J. Wilson, journalist Jamie Bartlett, counter-terrorism expert Mubin Shaikh, and educator Shabana Basij-Rasikh.

Sometimes, being truthful can be uncomfortable — even risky. But can radical honesty and openness change things for the better? This hour, TED speakers take transparency all the way to its limit. Guests include business writer David Burkus, entrepreneur Ray Dalio, journalist Trevor Timm, and hospital-patient liaison Leilani Schweitzer.

Sometimes, the best solutions to complex problems are simple. But simple doesn't always mean easy. This hour, TED speakers describe the innovation and hard work that goes into achieving simplicity. Guests include designer Mileha Soneji, chef Sam Kass, sleep researcher Wendy Troxel, public health advocate Myriam Sidibe, and engineer Amos Winter.

Art can evoke powerful feelings. But can it do more? This hour, TED speakers share ideas on the transformative nature of art and its ability to shape the way we see ourselves and the world around us. Guests include painter and sculptor Titus Kaphar, painters Dre Urhahn and eL Seed, textile artist Magda Sayeg, and conductor Benjamin Zander.