Horizon uncovers the secret world of our dreams. In a series of cutting-edge experiments and personal stories, we go in search of the science behind this most enduring mystery and ask: where do dreams come from? Do they have meaning? And ultimately, why do we dream?

What is wrong with nudity? Why are people embarrassed about their bodies? How and why did they get the way they are?

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.

In part three of this landmark series from Norma Percy and the team that made the multi-award winning documentaries The Death of Yugoslavia and Elusive Peace: Israel and the Arabs, contributors, including Iran's President Khatami, tell the inside story of the West's continuing nuclear confrontation with Iran. The film also shows a rare moment when they worked together.

Militant Islam enjoyed its first modern triumph with the arrival in power of Ayatollah Khomeini in Iran in 1979. In this series of three programmes, key figures tell the inside story.

Every summer in the seas off Alaska humpback whales, sea lions and killer whales depend on an explosion of plant life, the plankton bloom. It tranforms these seas into the richest on Earth. But will these animals survive to enjoy the great feast?

The great flood in the Okavango turns 4,000 square miles of arid plains into a beautiful wetland. Elephant mothers guide their families on an epic trek across the harsh Kalahari Desert towards it, siphoning fresh water from stagnant pools and facing hungry lions. Hippos battle for territory, as the magical water draws in thousands of buffalo and birds, and vast clouds of dragonflies. Will the young elephant calves survive to reach this grassland paradise?

A mighty army of dolphins, sharks, whales, seals and gannets hunt down the billions of sardines along South Africa\'s east coast each winter. This is the Sardine Run: an underwater Armageddon, the greatest gathering of predators anywhere on the planet, and the most spectacular event in the world\'s oceans.

Each year more than one million wildebeest and zebra invade the Serengeti grasslands, making it a paradise for the predators that live there. But what happens when the herds move off again? We follow the moving story of one lion family\'s struggle to survive until the return of the great migration. Nature\'s Great Events tells the story of the epic trek of herds that follow the rains to fresh pastures, and the tale of the predators they leave behind.

Every year grizzly bear families in North America depend for their survival on a spectacular natural event: the return of hundreds of millions of salmon from the Pacific Ocean to the mountain streams where they were born. The salmon travel thousands of miles to spawn and then die.

The great flood in the Okavango turns 4,000 square miles of arid plains into a beautiful wetland. Elephant mothers guide their families on an epic trek across the harsh Kalahari Desert towards it, siphoning fresh water from stagnant pools and facing hungry lions. Hippos battle for territory, as the magical water draws in thousands of buffalo and birds, and vast clouds of dragonflies. Will the young elephant calves survive to reach this grassland paradise?

In the flooded forests of the Peruvian Amazon lives one of the world\'s rarest and most mysterious primates, the red-faced uakari monkey. Local people call them English monkeys because of their resemblance to sunburnt visitors. Now there is a new Englishman on the scene, Mark Bowler, a young biologist who battles through the forest in his quest to understand the monkeys\' secret lives.

Wildlife film maker Rebecca Hosking investigates how to transform her family\'s farm in Devon into a low energy farm for the future, and discovers that nature holds the key.

Botswana\'s elephants are doing very well, too well perhaps. People are worried that too many elephants will damage their fragile desert home and have suggested that up to 60,000 should be culled. Researcher Mike Chase studies ancient elephant migration routes - he has tracked them across vast deserts, desolate salt pans, and Angolan minefields. Now he thinks he has a plan that could safeguard their future.

Acclaimed war correspondent Rageh Omaar examines the effect the Crusades have on the world today. In the West, the Crusades are a chapter of Christian history that has little impact on our everyday lives, but in the Middle East many believe that the Crusades are happening again.

Leading British writer Howard Jacobson, a Jew himself, examines the origins and consequences of Christian belief. He argues that although Christianity originated in devout Judaism, for Jews it has been, for the most part, a calamity.

The world is affected by an obesity epidemic, but why is it that not everyone is succumbing? Medical science has been obsessed with this subject and is coming up with some unexpected answers. As it turns out, it is not all about exercise and diet. At the centre of this programme is a controversial overeating experiment that aims to identify exactly what it is about some people that makes it hard for them to bulk up.

Whether it’s English, Spanish, Chinese, or Urdu, babies and young children are able to pick up their native language with remarkable ease; no one language seems any more difficult than any other. Yet few children who are taught a language in school have anything to show for it when they grow up. Why is learning a second or third language so difficult?

This World has gained rare access to Nelson Mandela, after years of retirement from public life.

In a special one-hour edition of the Money Programme, Fiona Bruce presents the definitive profile of Bill Gates as he embarks on his latest challenge - giving away the billions he has amassed, through the charitable foundation he runs with his wife and his father.

Extraordinary photography reveals the incredible swarm intelligence that lies behind animal invasions.

Jon Blair's Oscar-winning documentary is the first ever eye-witness account of the life and legacy of the iconic child diarist, Anne Frank.

Documentary which tells the story of evolution theory since Darwin postulated it in 1859 in 'On the Origin of Species'.

At least 34 teenagers were stabbed to death last year in the UK. In just a decade, the number sentenced for carrying a knife has risen ten-fold. So why are so many of Britain's youngsters arming themselves with knives? And why do some kill?

Frank Skinner is one of Britain's most controversial comedians but even he felt the comments broadcast last year by Jonathan Ross and Russell Brand on BBC Radio went too far. As he experiments with reducing the expletive count in his own stand-up show, Frank sets out to discover if the Ross-Brand storm really was a watershed in broadcasting's debate about bad language and offence.

Jeremy Vine reveals the problem of sexual bullying in our schools and hears from experts, parents and teachers - but most importantly from the kids themselves - on what we can do to tackle it.

This moving film reveals the differing fortunes of a mother polar bear and a mother grizzly bear, and their new-born cubs, in a rapidly-changing world. The shrinking Arctic ice may be making life much tougher for polar bears, but it is offering new opportunities for grizzly bears to the south.

Tiger experts in Bangladesh have a problem: how can they encourage local people to protect the beautiful and endangered Bengal Tiger when these animals have developed a taste for human flesh?

Mark Meakin attempts to unravel the mysterious wanderings of the biggest fish in the sea.

Just how does the cuckoo trick other birds into accepting its eggs and raising its young? In this film, new photography is combined with archive footage and the latest scientific findings to solve a puzzle which, as narrator David Attenborough explains, has perplexed nature-watchers for thousands of years.