Science Fiction (SF) can be a difficult genre to define. English Professor Emeritus and SF author James Gunn probably said it best, “Science fiction is the literature of change.”

SF can be differentiated from Fantasy by its reliance on rationality and reason. The Fantasy author asks the reader to suspend disbelief, while the SF author persuades the reader to understand.

Hard SF, then, is the sub-genre that is the most rational, the most reasonable.

It gets its name from the so-called hard sciences which operate via the scientific method, e.g., physics, chemistry, biology, astronomy, geology. Hard SF is often written by real-life scientists/engineers and often features scientist/astronaut/engineer protagonists.

Furthermore, hard SF is often didactic; it tries to teach the reader some real-life science/engineering.

Here, rather than a strict numerical ranking, I group hard SF novels into several main categories, based on what type of science readers might learn: physics, astronomy/astronautics, math/computer science, climate science and biology/genetic engineering. The novels listed tend to skew towards more recent works because hard SF novels can become out-of-date as science progresses.

It should be noted, each author was limited to only one entry in the list below; often, an author has written several hard SF novels that could qualify as ‘best.’