WHYY-FM (90.9 MHz, "91 FM") is a public radio station licensed to serve Philadelphia, Pennsylvania. Its broadcast tower is located in the city's Roxborough section of the city at (40°2′30.9″N 75°14′21.9″W / 40.041917°N 75.239417°W / 40.041917; -75.239417) while its studios and offices are located on Independence Mall in Center City Philadelphia. The station, owned by WHYY, Inc., is a charter member of NPR and contributes several programs to the national network.

WHYY signed on the air on December 14, 1954, owned by the Metropolitan Philadelphia Educational Radio and Television Corporation. It was the first educational station in Philadelphia. The transmitter, originally located at 17th and Sansom Streets in Philadelphia, was donated by Westinghouse Broadcasting. In 1957, it added a sister television station, WHYY-TV on channel 35.

In 1963, WHYY-TV moved from channel 35 in Philadelphia to the stronger channel 12 in Wilmington, Delaware. At the time, Federal Communications Commission (FCC) regulations did not allow co-owned stations in different broadcast services to share the same base callsign if they did not have the same or adjoining city of license. As a result, the radio station was forced to change its call sign and became WUHY-FM to match the renamed WUHY-TV on channel 35. The FCC removed this restriction in 1983 and the radio station was allowed to reclaim the WHYY-FM calls.

When NPR was formed in 1970, the station became a charter member and was one of the 90 stations that carried the initial broadcast of All Things Considered.

• NPR: Fresh Air with Terry Gross and Tonya Mosley, a Peabody Award–winning weekday magazine of contemporary arts and issues, is one of public radio's most popular programs. 5.3 million people listen to the broadcast on 640 National Public Radio stations across the country, as well as in Europe on the World Radio Network. The program originated in 1975 as a local show before going national in 1987.
• Radio Times With Marty Moss-Coane, a daily hour-long program that tackles a wide range of issues.
• The Pulse is a show that focuses on stories at the heart of health, science and innovation in the Philadelphia region. The show is hosted by WHYY's Behavioral Health Reporter Maiken Scott and distributed on the Public Radio Exchange.

Until 1990, WHYY served the region as a non-commercial station with a format that featured mostly classical music with some jazz and folk music. The management decision to establish a news/talk radio format was a departure from the classical music that most public radio stations were programming. The format switch left the privately owned WFLN as the only Philadelphia classical station and resulted in protests from many of the station's listening audience who were among WHYY's major contributors. After WFLN's new owners also abandoned the classical format in the late 1990s, Temple University's WRTI (90.1 FM) began programming classical music during the day to serve the displaced listeners.

On June 6, 2011, the New Jersey Public Broadcasting Authority agreed to sell five FM stations in Southern New Jersey to WHYY. The purchase was made through an anonymous one-million dollar grant and a non-cash agreement that included scholarships for students and teachers. The five stations were previously the southern portion of the New Jersey Network's statewide radio service.

The transaction was announced by Governor Chris Christie, as part of his long-term goal to end state-subsidized public broadcasting. The governor's critics maintained that scrapping New Jersey Network effectively ended all non-commercial statewide news coverage. It was also noted that the sale eliminated a source of legislative oversight frequently critical of the Christie administration.

WHYY assumed control of the stations through a management agreement on July 1, 2011, pending FCC approval for the acquisition. At that point, the stations began to simulcast WHYY-FM programming. The five stations are:

Call sign	Frequency	City of license	FID	ERP (W)	HAAT	Class	Transmitter coordinates	FCC info
WNJB-FM	89.3 FM	Bridgeton, New Jersey	48934	2,500 vert 1 horiz	67 m (220 ft)	A	39°27′35.4″N 75°9′26.7″W / 39.459833°N 75.157417°W / 39.459833; -75.157417 (WNJB-FM)	LMS
WNJM	89.9 FM	Manahawkin, New Jersey	48460	250 vert 1 horiz	69.5 m (228 ft)	A	39°41′53.4″N 74°14′4.5″W / 39.698167°N 74.234583°W / 39.698167; -74.234583 (WNJM)	LMS
WNJN-FM	89.7 FM	Atlantic City, New Jersey	48483	6,000 vert 25 horiz	84 m (276 ft)	A	39°27′40.4″N 74°41′4.5″W / 39.461222°N 74.684583°W / 39.461222; -74.684583 (WNJN-FM)	LMS
WNJS-FM	88.1 FM	Berlin, New Jersey	48486	80 vert 1 horiz	287 m (942 ft)	A	39°43′41.4″N 74°50′37.6″W / 39.728167°N 74.843778°W / 39.728167; -74.843778 (WTHA)	LMS
WNJZ	90.3 FM	Cape May Court House, New Jersey	48464	6,000	72 m (236 ft)	A	39°06′18.4″N 74°48′4.6″W / 39.105111°N 74.801278°W / 39.105111; -74.801278 (WNJZ)	LMS

The stations all operate at relatively low power due to the crowded state of the noncommercial end of the FM dial in the northeastern United States. They primarily serve areas of southern New Jersey not covered by the main WHYY-FM signal, which itself operates at a relatively modest 13,500 watts. However, their combined footprint extends WHYY-FM's coverage from Berks County to the Jersey Shore.

In November 2022, WHYY began to reduce its New Jersey radio footprint by announcing that it would sell WNJB-FM to non-profit Christian Broadcast, The Bridge of Hope, Inc., which owns WKNZ in Harrington, Delaware. The sale was approved by the FCC and was later completed in February 2023.

In March 2023, WHYY also announced that it would sell WNJS-FM to the Bux-Mont Educational Radio Association which owns WRDV for $110,000. The sale of the station was consummated on June 15, 2023.

In April 2019, WHYY acquired local news website Billy Penn. At its 2014 founding, the site was conceived as a "mobile-first" site packaging local news for millennials. The purchase was compared to New York public radio station WNYC buying the Gothamist in February 2018.

• WHYY-TV

• Official website
• Facility details for Facility ID 72336 (WHYY-FM) in the FCC Licensing and Management System
• WHYY-FM in Nielsen Audio's FM station database
• Facility details for Facility ID 48934 (WNJB-FM) in the FCC Licensing and Management System
• WNJB-FM in Nielsen Audio's FM station database
• Facility details for Facility ID 48460 (WNJM) in the FCC Licensing and Management System
• WNJM in Nielsen Audio's FM station database
• Facility details for Facility ID 48483 (WNJN-FM) in the FCC Licensing and Management System
• WNJN-FM in Nielsen Audio's FM station database
• Facility details for Facility ID 48464 (WNJZ) in the FCC Licensing and Management System
• WNJZ in Nielsen Audio's FM station database