The main theses of the book include (1) a late Neolithic or earlier discovery of the precession of the equinoxes[2] and (2) an associated long-lived megalith-building late Neolithic civilization that made astronomical observations sufficient for that discovery in the Near East,[2] and (3) that the knowledge of this civilization about precession and the associated astrological ages was encoded in mythology, typically in the form of a story relating to a millstone and a young protagonist.

[19] Santillana and Dechend state in their introduction to Hamlet's Mill that they are well aware of contrasting modern interpretations of myth and folklore but find them shallow and lacking insight: "...the experts now are benighted by the current folk fantasy, which is the belief that they are beyond all this – critics without nonsense and extremely wise".

[21][27][28][22] The Origins of Scientific Thought anticipated Hamlet's Mill's arguments as in this quotation: "We can see then, how so many myths, fantastic and arbitrary in semblance, of which the Greek tale of the Argonaut is a late offspring, may provide a terminology of image motifs, a kind of code which is beginning to be broken.

[27] Hamlet's Mill was severely criticized by notable academic reviewers[33][34][35][36] on a number of grounds: tenuous arguments based on incorrect or outdated linguistic information;[37] lack of familiarity with modern sources;[38] an over-reliance on coincidence or analogy;[39] and the general implausibility of a far-flung and influential civilization existing and not leaving behind solid evidence.

There are frequent flashes of insight, for example, on the cyclical world views of the ancients and on the nature of mythical language, as well as genuinely eloquent, quasi-poetic homilies.Writing in The New York Review of Books, Edmund Leach (1970) noted: [The] authors' insistence that between about 4000 B.C.

R. Ellis Davidson (1974) referred to Hamlet’s Mill as: [...] amateurish in the worst sense, jumping to wild conclusions without any knowledge of the historical value of the sources or of previous work done.

On the Scandinavian side there is heavy dependence on the fantasies of Rydberg, writing in the last [19th] century, and apparent ignorance of progress made since his time.In contrast, others praised Hamlet's Mill.

[40][41][42][43] The astrophysicist Philip Morrison, a friend of Santillana's,[22] began with criticism but concluded "here is a book for the wise, however it may appear," for a review in Scientific American.

[43] The Swedish astronomer Peter Nilson, while stating that Hamlet's Mill is not a work of science, expressed admiration for it and credited it as a source of inspiration when he wrote his own book on classic mythologies based on the night sky: Himlavalvets sällsamheter (1977).