Philadelphia's three senior "villages" — virtual senior communities — are joining more than 100 others across the country to celebrate the 15th anniversary of the movement this year.

Here in Philly, senior villages will mark the occasion with a live telecast Monday, Sept. 25, featuring Atul Gawande, physician and best-selling author of Being Mortal, presented by Beacon Hill Village of Boston and the Village to Village Network at the Parkway Central Library, 1901 Vine St., Skyline Room, fourth floor.

Gawande, who interviewed members of the Beacon Hill Village for his book, will speak from 4:30 to 6 p.m. The event is free, but registration is required; email info@eastfallsvillage.org or call 215-589-4344.

Villages are networks of seniors who live near one another and want to remain in their own homes and communities, rather than move and enter retirement or nursing homes. The movement began in Boston with the founding of Beacon Hill Village in 2002.

Currently, there are 220 villages operating in the United States and 100 villages in development nationally, with 40,000 Americans listed as members in 45 states and the District of Columbia.

Three main villages currently serve seniors in Philadelphia: East Falls Village; Northwest Village Network, serving Northwest Philly; and Penn's Village in Center City. The 600 or so members join for a small fee and have an on-call phone number, access to vetted home-repair contractors, and rides to doctors and other appointments. Anyone in the service area can join, regardless of age.

"This event provides an opportunity to promote our three villages in Philadelphia, but also to connect those in the Philadelphia area who may be interested in starting a village," said Mary Flournoy, a cochair of East Falls Village.

"We are proud members of a movement redefining aging," said Jane Eleey, executive director of Penn's Village.

For those who aren't familiar with the concept, the event will be able to answer a lot of questions, as well as offer information about the Village to Village Network, founded in 2010, which provides support nationwide to those interested in starting villages.

Gawande's book has inspired many conversations about the end of life. In Being Mortal, he tackles the challenge of his profession: how medicine and doctors not only can improve life but also the process of its ending. He examines senior villages vs. nursing homes and hospice care, and, in the book, he included Beacon Hill Village and the village model as an example of the value of community and choice as Americans grow older.

A renowned public-health researcher, Gawande describes seniors' efforts to "maintain autonomy as they age in the face of ingrained habits, cultural expectations, and one-size-fits-all corporate offerings," Flournoy said.

Over the last 15 years, virtual villages have become a more viable option for older adults in their later years, providing services and extending community to people who want to remain in their own homes and enjoy a rich stew of activities.

One of America's pressing issues is how to support and care for aging populations. By 2030, 20 percent of the U.S. population will be over 65, an estimated 83 million people. By 2050, the number of people 65 or older is projected to increase 120 percent, to more than 88 million, or nearly one in five.

The number of Americans 85 or older will more than triple over the same period, to 19 million, according to "Housing an Aging Population," a report by the Center for Housing Policy, the research arm of the nonprofit National Housing Conference in Washington.

There's also senior cohousing, in which older adults choose to live in the same house, same building, or same neighborhood and share expenses and services, such as rides to doctors and home repair. Today, there are more than 700 cohousing neighborhoods in Denmark and other European countries, and close to 150 in the United States.

In Pennsylvania, a handful of cohousing projects are forming: Altair Ecovillage in Kimberton, Concord Ecovillage in Kennett Square, Harmony Green Village in the King of Prussia area, Three Groves Ecovillage in West Grove, and Wissahickon Village Cohousing in Mount Airy.

Following is contact information for the local villages in the Philadelphia and central New Jersey areas:

• Penn's Village (www.pennsvillage.org), 201 S. 21st St., Philadelphia, 19103; 215-925-7333.

• East Falls Village (eastfallsvillage.org), Box 12672, Philadelphia, 19129;  267-444-4507; operating group cochairs Mary Flournoy, Phil Hineline.

• Northwest Village Network (www.northwestvillagenetwork.org); 7130 Cresheim Rd., Philadelphia, 19119; 215-247-0457; chair Peter Javsicas.

• Community Without Walls (cwwprinceton.org); info@cwwprinceton.org.