2015 has brought a constant stream of news about podcasts — but ingesting said news at the micro/announcement level makes it difficult to pick out larger trends trends. That’s why we run Nicholas Quah’s weekly podcast column Hot Pod, to keep you updated on the space and draw together some of these bits of information.

It’s also why a new report by Tow Center for Digital Journalism fellow Vanessa Quirk is so valuable. The report looks at the current state of business models in the podcasting industry, contextualizing them with a history of the space and a cool interactive timeline. You can read the full report here.

Quirk’s report is particularly helpful in breaking down the business models that different types of podcasts are using. She lists some of these models in a section toward the end of the report, “Operating Philosophies.”

These aren’t “hard and fast” categories, she writes, but instead “general ‘philosophies’ that influence the ways podcasts raise revenue and prioritize revenue streams.”

— Universal: Reach everyone we can. Examples: This American Life, New York Public Radio, Intelligence Squared.

“We don’t want to have a paywall on the actual content because that goes against the idea of having the largest audience possible to hear what we feel are important stories,” Seth Lind, director of operations at This American Life, told Quirk.

“Universal” podcasts use a number of different revenue streams, including direct support and foundation grants, but “rely quite heavily on both baked-in and dynamic advertising.”

— Premium: Create relationship/engage with audience. Examples: Gimlet Media, Earwolf (Howl), Slate (Slate Plus), 99% Invisible

Podcasts and networks in this category “seek to cultivate relationships with their audiences and grow more ‘premium’ experiences.” Though the podcasts themselves may be free to listen to, donations or subscriptions are encouraged.

“The majority of people who join [Slate Plus] are podcast listeners,” Andy Bowers, chief content officer of Panoply Media Group, told Quirk. “They get VIP tickets to live shows and come to meet the hosts. They’re our hardcore fans.”

Quirk adds that “Podcasts that operate under this philosophy, but without subscriptions (perhaps because they also operate under a universal philosophy), rely heavily on live events and crowdfunding campaigns to galvanize listeners and foster a sense of community.”

— Value Added: Diversify content/brand. Examples: BuzzFeed, Audible, Panoply (podcasts add value to publishing partners)

Under this model, “podcasts are seen as a way of adding value to both the consumer base and the network’s brand…For example, Audible, known for its audiobooks, is currently building up an arsenal of high-quality, original content in order to ‘enhance’ its offerings for its subscribers.”

Jenna Weiss-Berman, director of audio at BuzzFeed, explained to Quirk why BuzzFeed’s podcasts don’t have to go viral:

We’re not trying to get 10 million listens. We have things on the site that easily get 10 million hits. We’re trying to do something that shows that BuzzFeed has many different sides. We’re trying to dive deeper…That’s what BuzzFeed is great at — the things that make a bunch of money can support the things that make less money.

The full report is here.