Harder is a surname. Notable people with the surname include:

• Ashley Harder
• Christopher Harder
• Fred Harder
• Elaine Harder (1947-2013), American politician
• Friedrich Harder (1891–1944), German SS-Hauptscharführer in Auschwitz concentration camp
• George Harder
• Hauke Harder
• Heinrich Harder
• Hieronymus Harder (1523–1607) German botanist
• James Harder
• Jan Harder
• Josh Harder, American politician
• Kelsie B. Harder
• Mel Harder
• Pat Harder
• Pernille Harder (disambiguation)
• Rhea Harder
• Robert Harder, American politician

• Sleppy-Burnquist House
• Sleppy House
• Sl eps
• Slepsek
• Slepče
• Slepšek
• SLERA
• S. Lesceux
• Slesvig-Holsten
• Slesvigske Fodregiment
• Sleswig-Holsteen
• Sleszynski-Pringsheim theorem
• Sleszynski–Pringsheim theorem
• Sleszynsky-Pringsheim theorem
• Sleszynsky–Pringsheim theorem
• Sletta Church (Froya)
• Sletta, Hordaland
• Slettebakken Church
• S (letter)
• Sletterhage Lighthouse
• Slettheia
• Slettmarkhoe
• Slettnes fyr
• Slettnes fyrstasjon
• Slettnes Lighthouse