Adelphi University is a private university in Garden City, New York. Adelphi also has centers in Downtown Brooklyn, Hudson Valley, and Suffolk County in addition to a virtual, online campus for remote students. It is the oldest institution of higher education in suburban Long Island. As of 2019, it had about 7,859 undergraduate and graduate students.

Adelphi University began with the Adelphi Academy, founded in Brooklyn, New York in 1863. The academy was a private preparatory school located at 412 Adelphi Street, in the Fort Greene neighborhood of Brooklyn, but later moved to Clinton Hill. It was formally chartered in 1869 by the board of trustees of the City of Brooklyn for establishing "a first class institution for the broadest and most thorough training, and to make its advantages as accessible as possible to the largest numbers of our population." One of the teachers at the Adelphi Academy was Harlan Fiske Stone, who later served as the Chief Justice of the United States.

In 1893, Charles Herbert Levermore was appointed as the head of Adelphi Academy. Seeking to establish a liberal arts college for the City of Brooklyn, Levermore received a charter from the Board of Regents of the State of New York, officially establishing Adelphi College on June 24, 1896. The college received its charter through the efforts of Timothy Woodruff, former Lieutenant Governor of New York and future first president of the board of trustees. Adelphi was one of the first coeducational institutions to receive a charter from the State of New York. At the time of its foundation, the college numbered only 57 students and 16 instructors. The Adelphi Academy continued to exist as a separate but nonetheless connected entity to the college. The new college was located in a building behind the Adelphi Academy, on the corner of St. James's Place and Clifton Place, in Brooklyn. The building that originally housed Adelphi is now used by Pratt Institute for their School of Architecture.In 1912, Adelphi became a women's college. In 1922, the school raised over one million dollars to expand the overcrowded facilities in Brooklyn. In 1925, Adelphi College severed its ties with the Adelphi Academy, the latter closing in 1930. In 1929, the college moved from its founding location in Brooklyn to the current location of its main campus in Garden City, New York. The original "academy" continues to function as a P–12 school in Brooklyn. The original three buildings of the Garden City campus, Levermore Hall, Blodgett Hall and Woodruff Hall, were designed by McKim, Mead and White.

In 1938, the Dance Program was founded by the world-famous dancer Ruth St. Denis. In 1943, the School of Nursing was established in response to the need for nurses due to American involvement in World War II. First Lady Eleanor Roosevelt presided over the opening of two federally funded residence halls on campus, in a speech entitled "The Challenge of Nursing for Young Women Today."

In 1946, after World War II ended, Adelphi reverted to a coeducational college and started admitting new students on the federal GI Bill. New sports teams were created following the readmission of men to the school. In 1952, the first program for clinical psychology was established at the school; it was the forerunner to the Institute for Advanced Psychological Studies, now the Gordon F. Derner School of Psychology.

In 1963, the New York State Board of Regents granted the college university status, and the name was changed to Adelphi University. In 1964, the School of Business was founded. In 1966, the Institute for Advanced Psychological Studies was founded. In 1973, the university established ABLE (Adult Baccalaureate Learning Experience) for the education of adults. Now known as the College of Professional and Continuing Studies, it was one of the earliest programs created for nontraditional students. In 1984, the Institute for Teaching and Educational Studies was founded; it became the School of Education in 1990. In 1993, the Society of Mentors was established, giving students faculty advisors that they could consult on an as-needed basis to assist them in their studies. In 1995, the Honors College was founded.

In January 1963, Adelphi Suffolk College (which had started out in 1955 offering extension courses in Suffolk County, New York) purchased the former W.K. Vanderbilt estate in Oakdale, New York. In 1968, it was spun off to Dowling College after its chief benefactor, Robert Dowling.

Adelphi faced a serious scandal in 1996, as the school celebrated its 100th anniversary. University president Peter Diamandopoulos and the board of trustees were accused of neglect of duty, misconduct and failure to carry out the educational purposes of Adelphi. The New York State Board of Regents was called in to investigate; Diamandopoulos, along with all but one of the board of trustees, was dismissed from office. The university was in dire financial straits until Robert A. Scott was installed in the position of President in 2000. Scott saved the school by decreasing tuition, increasing scholarships offered for the students, and launching an advertising campaign to increase enrollment. Since that time, the school has surpassed many of its previous gains, and is said to be undergoing a new renaissance. Adelphi University has been ranked as a "Best Buy" college by the Fiske Guide to Colleges for the last ten years for its quality education offered at a comparatively affordable price. Adelphi University also participates in the National Association of Independent Colleges and Universities's (NAICU) University and College Accountability Network (U-CAN). In 2023, the Princeton Review ranked Adelphi University a "Green College" making the list of environmentally responsible colleges and universities across the country.

In August 2023, Adelphi relocated the Manhattan Center location to Downtown Brooklyn at 179 Livingston Street. Adelphi - Brooklyn Center, located on the 5th through 7th floors, is adjacent to Macy's Brooklyn store and shared with St. Francis College.

The university's School of Social Work is home to the Adelphi New York Statewide Breast Cancer Hotline and Support Program The program began in 1980 as the Woman-to-Woman Hotline, a free and confidential service to help women with breast cancer. It is the second oldest breast cancer hotline in the United States; over 100 trained volunteers offer information and emotional support for women and men suffering from breast cancer. There are professional social workers, bi-lingual Spanish-speaking staff and support staff, along with support groups, educational programs and individual counseling.

Academic rankings
National
Forbes	353
U.S. News & World Report	166
Washington Monthly	238
WSJ/College Pulse	208
Global
THE	1501+

In 2015, Adelphi University was ranked #17 in New York State by average professor salaries.

In 2024 Adelphi University was ranked No. 163 in National Universities by U.S. News & World Report.

• College of Arts and Sciences: B.A., B.S., B.F.A., M.A., M.S., M.F.A.,
• College of Professional and Continuing Studies: A.A., A.S., A.A.S., B.A., B.S., Post-baccalaureate Certificate, M.S.
• Gordon F. Derner School of Psychology: B.A., M.A., M.S., Ph.D., Psy.D.
• Ruth S. Ammon School of Education: B.A., B.S., M.A., Advanced Certificates, Au.D., Ph.D.
• Robert B Willumstad School of Business: B.S., B.A., B.B.A., M.S., M.B.A., M.S./M.B.A. (with School of Nursing).
• College of Nursing and Public Health: B.S., M.S., M.S./M.B.A. (with School of Business), Ph.D.
• School of Social Work: B.S.W., M.S.W., D.S.W., Ph.D.
• Honors College

On February 27, 2012, president Robert A. Scott announced a gift of $9.5 million from Adelphi Board of Trustees Chairman Robert B. Willumstad '05 (Hon.). The Adelphi University School of Business, established in 1964, was renamed the Robert B. Willumstad School of Business in his honor.

• Dentistry: New York University College of Dentistry (3–4 B.S./D.D.S.)
• Engineering: Columbia University,(3–2 B.A./B.S.)
• Environmental Studies: Columbia University (3–2 B.A./B.S. or 4–2 B.A./M.S.)
• Optometry: SUNY State College of Optometry (3–4 B.S./O.D.)
• Osteopathic Medicine: Touro College of Osteopathic Medicine (3–4 B.S./D.O.)
• Physical Therapy: New York Medical College (4–3 B.S./D.P.T.)

Adelphi has partnerships with outside providers who offer study abroad opportunities to students in approximately 120 countries.

For semester and academic year direct exchanges with Adelphi partners, students may use 100% of their federal and institutional aid. For programs which are not directly associated with Adelphi (from accredited institutions and are approved by the Center for International Education), students may use all their federal aid, and 75% of their Adelphi institutional aid — while remaining enrolled on campus. Adelphi faculty-led programs, including theater, art, art history, literature, history, counseling, chemistry and speech-pathology, are held in Italy, Kenya, Denmark, Norway, Finland, Iceland, England, Jamaica, Kosovo and Poland.

Many of the buildings on the Garden City campus are symmetrical in nature. This is likely because garden cities are typically planned symmetrically. For example, Woodruff Hall has a second chimney solely to preserve the symmetry of the building.

• Alice Brown Early Learning Center

• Delta Sigma Pi

The Adelphi Panthers are the athletic teams of Adelphi University. The Panthers compete at the NCAA Division II level for all sports and have been a member of the Northeast-10 Conference since 2009.

The Panthers have won 18 NCAA Division II National Championships in three different sports. The men's lacrosse team has won seven national crowns, their last coming in 2001. The women's lacrosse team has won an NCAA Division II-record ten, including three consecutive National Championships in 2009, 2010, 2011 and back-to-back titles in 2014 and 2015; and most recently in 2019. In 1974, the men's soccer team were the National Champions. They have also won numerous individual national championships in track and field.

Since transitioning to the Northeast-10, the Adelphi Panthers have become a powerhouse in the East Region. In 2013, just their fourth year in the conference, the Panthers were awarded the 2013 Northeast-10 Presidents' Cup. The Presidents' Cup is presented annually to signify overall athletic excellence in the Northeast-10. The honor is awarded to the institution that compiles the most total points from all of its programs competing in league championships.

• 
  Gary Dell'Abate ("Baba Booey"), producer of The Howard Stern Show
• 
  Sean Hannity, conservative news host
• 
  John J. Phelan Jr., former President of the New York Stock Exchange
• 
  Chuck Connors, actor and professional baseball and basketball player
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  Edolphus Towns, U.S. Congressman
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  Leona Marlin-Romeo, former Prime Minister of Sint Maarten
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  Flavor Flav, rapper
• 
  Paul Ekman, psychologist
• 
  Meredith Eaton, actress
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  Gregory Meeks, U.S. Congressman
• 
  Chuck D, rapper

• Gary Dell'Abate ("Baba Booey") (b. 1961) – producer of The Howard Stern Show
• John D. Wren – President, CEO, and Chairman Omnicom Group
• Joe Abbenda (b. 1939) – former Mr America and Mr Universe
• Chris Armas (b. 1972) – professional soccer player, Chicago Fire of Major League Soccer and Adelphi women's soccer coach
• Michael Balboni (b. 1959) – Deputy Secretary for Public Safety for the State of New York
• Bob Beamon (b. 1946) – American track and field athlete, world record holder in long jump
• Justin Vivian Bond – Actor, cabaret singer, named MacArthur Fellow 2024
• Ron Bruder – entrepreneur who runs Middle East education non-profits, named on the Time 100
• Dave Cayemitte – former soccer player, financial analyst
• Melanie Chartoff – actress and comedienne
• Linda Cimino – college basketball coach
• Chuck Connors – athlete and actor
• Nick Cummings – Ph.D. past president of the American Psychological Association and founding board chairman of Care Integra, and author
• Chuck D (Carlton Ridenhour; b. 1960) – musician, author, lecturer, founder and frontman of the hip-hop group Public Enemy
• Vyvyan Donner – fashion editor, film director, screenwriter, theatrical costume designer and caricaturist
• Meredith Eaton-Gilden – psychotherapist and actress
• Paul Ekman – psychologist
• Clara Fasano – sculptor
• Flavor Flav – rapper, member of rap group Public Enemy
• Ida M. Flynn (1942–2004), American computer scientist, textbook author, and professor
• John Forslund – television play-by-play announcer for the Seattle Kraken of the NHL
• Karen Fraction – Broadway dancer and actress
• Charles J. Fuschillo, Jr. – New York State Senator, 8th District
• Arie Gill-Glick – Israeli Olympic runner
• Malika Grayson – engineer, speaker, and author
• Wes Green – professional lacrosse player, Los Angeles Riptide of Major League Lacrosse, and San Jose Stealth of National Lacrosse League
• Alexander Greendale – playwright and civic leader
• Sean Hannity – Fox News host.
• Alice Hoffman – author
• Earlene Hill Hooper – New York State Assembly Assemblywoman, 18th District
• Jonathan Larson – creator of the Broadway musical Rent
• Michael Lindsay – actor and voice artist
• Suzanne Luna – producer and director on The Ellen DeGeneres Show
• Gee Malik Linton – director and screenwriter
• Leona Marlin-Romeo – 5th Prime Minister of Sint Maarten
• Gregory W. Meeks – congressman from New York, 6th District
• Sal Mineo, Actor, Academy Award Nominee
• Donna Orender (née Geils; born 1957) – women's pro basketball league all-star and former WNBA president
• Carmen Ortiz – former U.S. Attorney for the District of Massachusetts
• Billy Phillips – professional soccer player and coach
• Chad Prince (b. 1979) – professional soccer player and coach
• Carolynn Reid-Wallace (b. 1942) – 13th president of Fisk University (2001–2003); assistant secretary of education for postsecondary education (1991–1993)
• Ron Robinson – chemist
• Todd Robinson - Director, screenwriter
• Dinelia Rosa – psychologist and professor
• Rony Schneider – Israeli professional soccer player
• Erin Stern – IFBB fitness professional and figure competitor
• Gary Sullivan – USL professional soccer player, Long Island Rough Riders
• Helen Rand Thayer (1863–1935), social reformer
• Al Trautwig – sports announcer, member of the Adelphi Athletics Hall of Fame
• Mary L. Trump – psychologist and author, niece of Donald J. Trump
• Rebecca Tobey – sculptor
• Edolphus Towns (b. 1934) – congressman from New York, 10th District
• Nicholas Turturro - Actor
• Steven Vincent – Broadway choreographer, dancer, and teacher
• Max Weinberg (b. 1951) – drummer and television personality
• Isuri Wijesundara – actress
• Robert B. Willumstad – chairman and CEO, American International Group
• Mike Windischmann (b. 1965) – soccer, captain of the 1990 United States World Cup team
• Theresa Wolfson (1897–1972) – labor economist and educator, won the John Dewey Award of the League for Industrial Democracy
• Jacqueline Woodson (b. 1963) – author of children's literature, named MacArthur Fellow 2020
• Roby Young (b. 1942) – Israeli international soccer player, and captain of Hapoel Haifa

• Al Davis (1929–2011), former line coach for the Adelphi College football team 1950–51
• Loren Hightower (1927–2017) – dancer, Metropolitan Ballet, American Ballet Theatre, and Agnes de Mille Dance Theatre; regular performer with the Metropolitan Opera and Broadway musicals
• Allen Krebs, sacked for expressing political views in class and went on to found the Free University of New York
• William Cranston Lawton (1853–1941), professor of Greek
• Jerry March (1929–1997), organic chemist and professor of chemistry; authored March's Advanced Organic Chemistry text
• Paul Mattick Jr. (b. 1944), professor and chair of philosophy. Author of Business as Usual: The Economic Crisis and the Failure of Capitalism. Son of Paul Mattick Sr.
• Paul Moravec, 2004 Pulitzer Prize winner in music composition
• Frances Perkins, professor of sociology, Labor Secretary under Franklin D. Roosevelt
• Lawrence Raphael, professor of communication sciences and disorders
• Ruth Westheimer (born Karola Siegel, 1928; known as "Dr. Ruth") German-American sex therapist, talk show host, author, professor, Holocaust survivor, and former Haganah sniper.
• Jacques P. Barber Dean and Professor of Psychology

• WBAU – The former student-operated radio station that broadcast on 90.3 FM.

• Official website
• Official athletic website