One of Sagan's main purposes for both the book and the television series was to explain complex scientific ideas in a way that anyone interested in learning can understand.

Sagan also believed the television was one of the greatest teaching tools ever invented, so he wished to capitalize on his chance to educate the world.

[4] The book covers a broad range of topics, comprising Sagan's reflections on anthropological, cosmological, biological, historical, and astronomical matters from antiquity to contemporary times.

[8] The book, like the television series, contains a number of Cold War undertones including subtle references to self-destruction and the futility of the arms race.

[14] Though spurred in part by the popularity of the television series, Cosmos became a best-seller by its own regard, reaching hundreds of thousands of readers.

"[22] It also ushered in a dramatic increase in visibility for science books, opening up new options and readership for the previously fledgling genre.

He appeared on many television programs, wrote a regular column for Parade, and worked to continually advance the popularity of the science genre.

In The New York Times Book Review, novelist James Michener praised Cosmos as "a cleverly written, imaginatively illustrated summary of [Sagan's]... ruminations about our universe... His style is iridescent, with lights flashing upon unexpected juxtapositions of thought.

[28] David Whitehouse of the British Broadcasting Corporation went so far as to say that "there is not a book on astronomy – in fact not one on science – that comes close to the eloquence and intellectual sweep of Cosmos...