Tourism is an international industry worth trillions of dollars, which creates hundreds of millions of jobs worldwide — but that wasn’t always the case. In his book, “A History of Modern Tourism,” University of New England history professor Eric Zuelow walks us through the story of how we learned to love travel. From diplomacy, to new technologies like steam power, to a growing need for adventure and self-expression, tourism has become a global phenomenon with a huge impact on the places we love to visit and the environment.

When it comes to losing weight or maintaining a healthy diet, many of us have chosen to go either low-calorie or low-fat. But recent research has started to upend nutrition science, reframing our notions of “healthy” eating, according to Dariush Mozaffarian, a cardiologist and Dean of the Friedman School of Nutrition Science and Policy at Tufts University.

Mozaffarian explains why the science is changing, when a calorie isn’t just a calorie, how fat could be a lot better than we think, and why he believes that government should play a much bigger role in influencing our food choices.

There has been a continuous problem, dating back to founding of the United States, according to Jill Lepore, a professor of American history at Harvard University.

Lepore, the author of “These Truths: A History of the United States,” says Americans have had tremendous faith in the notion that technological innovations could heal our divisions and fix political problems. But that faith has frequently been misplaced or misguided. And ethical conversations around how to keep newspapers, radio, TV and other technologies in check, often come too late.

The heroism of D-Day is immortalized in history books, but far less attention is given to the individuals who worked undercover to prevent Germany from developing an atomic bomb during WWII. In his new book, The Bastard Brigade: The True Story of the Renegade Scientists and Spies Who Sabotaged the Nazi Atomic Bomb, science writer Sam Kean tells the stories of the men and women who made up the Alsos Mission, or the “Bastard Brigade.” They worked tirelessly to make sure Germany’s (impressive) scientific discoveries wouldn’t change the course of the war.

After Russia sent a man into space, the United States didn’t want to be left behind. But getting a man on the moon wasn’t as easy as just saying we would. David Meerman Scott, a marketing strategist and co-author of the book Marketing the Moon: The Selling of the Apollo Lunar Program talks about just what it took — from PR strategies to partnering with Walt Disney — to get enough support for the mission. Without the marketing and media attention, Scott thinks, we couldn’t have landed on the moon.

DARPA, the Defense Advanced Research Projects Agency, has been developing new military technologies for the United States since shortly after the launch of Sputnik in 1957. But Sharon Weinberger, the Washington Bureau Chief for Yahoo News and the author of The Imagineers of War: The Untold Story of DARPA, the Pentagon Agency that Changed the World, says there’s more to the Agency than new weapons and military strategies. DARPA, Weinberger explains, not only incubated the internet, but it has also worked on self-driving cars and extra-sensory perception, and explored the potential for developing super soldiers.

In recent years, some American cities, like Pittsburgh, have been transformed by legions of tech jobs. But even as these one-time industrial cities reinvented themselves, many residents - including those who are part of communities of color - have been excluded from the prosperity and growth that have been ushered in along with the influx of jobs and investment.

Andre Perry, a fellow in the Metropolitan Policy Program at the Brookings Institution, and Tawanna Black, founder and CEO of the Center for Economic Inclusion, explain some of the reasons for these sorts of disparities in wealth, wages and opportunity between minority and white communities, and propose a radically different way forward.

Plastics are colorful, shiny, and flexible. They can also be sturdy, monochrome, and opaque. They come in different shapes and sizes, too. In fact, we’ve become so good at creating and molding plastics into whatever we want them to be that author Susan Freinkel says: it’s hard to imagine a world without them. In her book, Plastics: A Toxic Love Story, Freinkel chronicles the history of plastics and explores how, for better or worse, the material shapes our lives.

When you hear the term “gig economy,” you probably think of Uber or Lyft or Postmates - companies that have used apps to disrupt industries and create an army of 1099 workers. But according to Louis Hyman, a Cornell University historian and author of Temp: How American Work, American Business, and the American Dream Became Temporary, the gig economy is a lot bigger than Silicon Valley. And it has a much longer history than you might think.

Back in the mid-19th century, some American entrepreneurs sailed halfway around the world - to China - to make their fortunes. These merchants would later build dynasties back home by investing money in promising American industries, including railroads and coal, as well as new technologies, like the telegraph.

It was the invention of the clipper ship that made it all possible. These were ships that were built for speed and profit, a profit that came not just by importing goods like tea to the U.S., but also by smuggling opium to China.

We talk with Steven Ujifusa, a historian and author of “Barons of the Sea: And their Race to Build the World's Fastest Clipper Ship,” about these vessels - which once raced across the ocean - and the owners who used them to reshape America.