The Wisconsin Book Festival is a celebration of reading that starts Thursday, centered at Madison’s Central Library. But organizers have come to see it as a year-round celebration culminating during four days in the fall.

On the eve of its milestone 15th anniversary, festival director Conor Moran describes how the free festival has grown from its start in 2002 to today.

The festival began as a four-day event, but has seen a tremendous amount of growth, particularly over the past three years, in the events held beyond those four days. And because of that, organizers can book big Wisconsin names and also well-known national writers.

In 2016, 15,500 people attended more than 100 events in the course of the year, with 10,000 of those coming over the four-day celebration.

“We’ve seen people from across an entire spectrum really come to understand what the book festival is about,” Moran said. And its not just Madison-area residents, but people from across the state.

Last year, the festival saw people from more than 100 municipalities in Wisconsin over the four-day event, and for the past two years it’s enjoyed coverage on C-SPAN’s Book TV.

“Those things weren’t part of the deal 10, 12, 15 years ago,” Moran said. “The growth has been staggering and I think that’s a testament to the space that we’re in. I think it’s a testament to the city we are in. It’s really a testament to the fact that people in Madison or wherever they are coming from, are coming to these things. They are buying books.”

The fact that so many people are taking part is giving Madison the reputation as a big book city and a cultural city, he said.

In the past, the festival has generally been in October, and the dates are dependent on the Badgers’ home football schedule, Moran said. “Always have been, probably always will be.”

The city’s annual Halloween celebration, Freakfest, is another consideration, making the options for this year’s book festival either the beginning of October or the beginning of November.

“We went with November because more stuff is published by then, and we thought it gave us a better chance to catch people once school had started,” Moran said.

Next year, it’s going to swing three weeks the other way, and will be held Oct. 11-14.

Besides Central Library, events will be in six other places. Over the four days, 73 author events are scheduled. Over the course of the year, that total rises to about 115.

Book lovers need to be strategic when mapping a course through the festival. Thursday’s highlights include Jeremi Suri talking about his book, “The Impossible Presidency,” which looks at why recent presidents have failed to bring bold change. Suri is a former UW-Madison professor who teaches global affairs at the University of Texas at Austin. His talk is at 5:30 p.m. at Central Library.

At 7 p.m. Thursday at Central Library, Gabrielle Langholtz will discuss “America: The Cookbook,” billed as a culinary road trip through the 50 states. She and her regional collaborators, Christine Muhlke and Ari Weinzweig, explore how each state’s history, culture and traditions define our diets.

At 4:30 p.m. Friday at Central Library, lawyers Susan Gloss, E.M. Kokie, Jay Ranney, Carl Rasmussen and Dean Strang discuss their second careers as writers. The session is titled “Lawyers Who Write.”

“Whether writing fiction, history, or biography, these lawyers have brought their research and evaluative skills to bear creating new works,” the program says.

Moran is particularly excited to have Amy Goldstein talk about her book, “Janesville: An American Story,” at 6 p.m. Saturday at Central Library. The longtime Washington Post reporter embeds herself in this south central Wisconsin city after the GM plant there closes, and documents the human fallout.

The book follows a group of people from 2008 to 2013. Even though its present-day epilogue shows an unemployment rate in the city at less than 4 percent, the book explores the drop in real wages, the divorces, and how partisan divisions are creating tensions where people used to get along.

A review in The New York Times ends with this: “‘Janesville’ is eye-opening, important, a diligent work of reportage. I am sure (Janesville Congressman) Paul Ryan will read it. I wonder what he will say.”

Moran is also thrilled to be bringing in author Angela J. Davis, who will be talking about her book, “Policing the Black Man: Arrest, Prosecution, and Imprisonment,” at 7:30 p.m. Friday at Central Library.

Angela J. Davis isn’t to be confused with Angela Y. Davis, the black power figure, author and academic known internationally for combating oppression.

Also an activist, Angela J. Davis is a law professor at American University in Washington, D.C., and a former director of the D.C. Public Defender Service. Her new book puts together 11 essays from scholars and criminal justice practitioners offering policy suggestions.

“That will be huge, I think,” Moran said. “It’s such a part of the Madison conversation and the national conversation. I think it will be a really moving event.”

Later in the month, Alexander McCall Smith is coming (7 p.m., Nov. 17) to talk about his book, “The House of Unexpected Sisters.”

Smith was a professor of medical law who worked in universities in the UK and elsewhere before starting his fiction-writing career, becoming hugely famous after coming out with “The No. 1 Ladies’ Detective Agency.” The series has sold more than 20 million copies — just in English alone.

Moran points to Smith’s visit as evidence the Wisconsin Book Festival is achieving its goal.

“We are hitting the ground and getting the traction that we need to get those kind of people to come,” he said.