Harry Turtledove is a writer whose bibliography spans science fiction, fantasy, historical fiction, and nonfiction. He has published under various pseudonyms, including Eric Iverson and H. N. Turteltaub, in addition to his own name. His works frequently delve into alternate history, exploring how pivotal historical events might have unfolded differently, such as the Confederacy winning the American Civil War or alien invasions occurring during World War II.

Turtledove's fantasy works often incorporate elements of magic into historical or pseudo-historical settings, examining large-scale conflicts and societal structures. His science fiction often features interstellar travel and encounters with alien species, as well as explorations of parallel timelines. He is also known for his young adult fiction series, Crosstime Traffic, which deals with interdimensional travel and its consequences, presented with a more restrained approach to mature themes. His writing style is characterized by detailed world-building and a focus on the consequences of historical and technological divergences.

A significant portion of Harry Turtledove's work, particularly under his own name, is dedicated to exploring alternate history. Series like 'Southern Victory' and 'Worldwar' examine large-scale geopolitical shifts resulting from altered historical outcomes. 'Southern Victory,' for instance, posits a Confederate victory in the American Civil War, leading to a vastly different 20th century. The 'Worldwar' series imagines an alien invasion during World War II, forcing humanity to unite against a common extraterrestrial foe and subsequently deal with the aftermath and colonization. These narratives often focus on the cascading effects of single historical turning points, exploring how societies, technologies, and international relations would evolve under drastically different circumstances.

Turtledove also crafts numerous fantasy worlds, often blending magical elements with historical or quasi-historical settings. The 'Videssos' series is set in a world analogous to the Byzantine Empire but infused with magic. Similarly, 'Darkness / Derlavai / World at War' presents a global conflict in a medieval-esque world where sorcery plays a role, drawing parallels to World War II. The 'War Between the Provinces' series reimagines the American Civil War with the addition of magic and altered geography. These works explore themes of warfare, societal structures, and the integration of fantastical elements into recognizable historical frameworks, often examining how magic might influence military strategy and political power.

Beyond grand historical or fantastical conflicts, Turtledove's writing frequently examines societal structures, identity, and the integration of different groups. The 'State of Jefferson Stories' series, for example, depicts a world where cryptids like Sasquatch and merfolk are real and integrated into human society. This series explores themes of cultural assimilation, racial stereotyping, and the challenges of coexistence between different species within a nation. The 'Atlantis' trilogy, set on a continent that separated from North America millions of years ago, also deals with the discovery and integration of a unique landmass and its inhabitants into world history, touching upon themes of exploration and divergence.