The world is affected by an obesity epidemic, but why isn't everyone succumbing? A controversial overeating experiment aims to identify why it's hard for some people to bulk up. This episode looks at what it is about some people that makes it hard for them to gain weight.

James Marsden looks at how cannabis use has affected different people's lives.

The series takes a look at dreams and as to why they are important to the cognitive process.

Professor Brian Cox takes a global journey in search of the energy source of the future. Called nuclear fusion, it is the process that fuels the sun and every other star in the universe. Yet despite over five decades of effort, scientists have been unable to get even a single watt of fusion electricity onto the grid. Brian returns to Horizon to find out why. Granted extraordinary access to the biggest and most ambitious fusion experiments on the planet, Brian travels to the USA to see a high security fusion bomb testing facility in action and is given a tour of the world's most powerful laser. In South Korea, he clambers inside the reaction chamber of K-Star, the world's first super-cooled, super-conducting fusion reactor where the fate of future fusion research will be decided.

The series takes a look at how the human body clock works and why certain things are more likely to happen at different times of the day.

The show examines the reasons why people are embarrassed by the naked human body.

The series attempts to show the best ways to survive a disaster by asking a team of experts for help.

David Baddiel explores the best ways to educate your children.

The series takes a look as to why science has been unable to predict when an earthquake is going to happen.

Ever since he was at school, actor and comedian Alan Davies has hated maths. And like many people, he is not much good at it either. But with the help of top mathematician Professor Marcus du Sautoy, Alan is going to embark on a maths odyssey. Together they visit the fourth dimension, cross the universe and explore the concept of infinity. But did his abilities peak 25 years ago when he got his grade C O-Level? Or will Alan be able to master the most complex maths concept there is?

What makes ordinary people commit extreme acts of violence? In a thought-provoking and disturbing journey, Michael Portillo investigates one of the darker sides of human nature

The intriguing possibility of life on Mars has fueled man's quest to visit the Red Planet. Drawing on 45 years of Horizon archive, space expert Dr Kevin Fong presents a documentary on Earth's near neighbor. Man's extraordinary attempts to reach Mars have pushed technological boundaries past their limit and raised the tantalizing prospect of establishing human colonies beyond our own planet. While the moon lies 240,000 miles away, Mars is at a distance of 50 million miles. Reaching the moon takes three days, but to land on Mars would take nearly eight months, and only two thirds of the missions to Mars have made it. The BBC has been there to analyze the highs and lows - including the ill-fated British attempt, the Beagle. Horizon has explored how scientists believe the only way to truly understand Mars is to send people there. If and when we do, it will be the most challenging trip humanity has ever undertaken.