This is the first book in Sitchin's monumental Earth Chronicles series. It is important to remember that fact because there is necessarily a lot of introductory material to be presented here in order to lay the foundation for what is to come. In other words, most of the really interesting stuff comes later in the series--Ancient Egypt, MesoAmerica, etc. Parts of this first book are somewhat dry and hard to get through. As one gets into the latter half, though, some pretty amazing arguments are made. If you read this book and no other, you may well have a hard time even sanctioning the kinds of ideas Sitchen presents, let alone believing them. When you read the rest of the series, though, the arguments are threshed out much more thoroughly and should at least lend an idea of possiblity to objective readers.
The idea that "ancient astronauts" (a term I dislike) had a hand in Man's creation and evolution is not new. Sitchin goes far beyond the normal arguments, however. He argues that there is an undiscovered planet in our own solar system upon which life developed and evolved millions of years before life on earth, a planet that seeded earth with its earliest life forms millions of years ago when this undiscovered planet entered our solar system and essentially crashed into a large planet between Mars and Jupiter--the planet in question was broken up into two parts, one eventually forming Earth and the other the asteroid belt. The 12th planet (counting the sun and moon as planets) he calls Nibiru; it is a planet with an eccentric orbit carrying it well past the other nine planets thousands of years at a time. Here life developed and advanced at a very early period. Needing resources, particularly gold, the planet sent forth emissaries to earth. In order to free themselves of the hard labor of mining, these aliens, the Nefilim, created Man by combining their genes with those of the ape men then on earth, a procedure made possible by the fact that the two races were in fact genetic cousins. Thus, the Nefilim became early man's gods, and their stories were told in the artifacts of the ancient Sumerians and of the kingdoms that came after them.
Sitchin makes a determined effort to tie Christianity and the Bible to the tale he unfolds. He effectively, and with good evidence, shows that the early stories in the Bible are based largely on older manuscripts from Sumeria. He explains many of the mysterious passages in the Bible by tying the stories to more complete Sumerian tales--the Elohim, the plural Deity mentioned in the Creation story, the great flood, the Tower of Babel, and others. In this endeavor, he is very successful. While one may not be convinced of his story of life on Earth, one cannot doubt the fact that the early books of the Bible are basically a condensed version of former manuscripts. He makes a convincing argument for his theories, but one will not be and should not be convinced based on this one book. Much supporting evidence is to be found in the later books in the series, where a far richer version of man's history is presented by the author. As unbelievable as many of his ideas sound, Sitchin actually does an effective job of answering many of the big questions that scientists and theologians have been unable to answer about life on earth, the most important of which is an explanation of why home sapiens developed so suddenly and miraculously 300,000 years ago. Right or wrong, his ideas answer a lot of questions and deserve serious study. Sitchin's knowledge of ancient civilizations is immense, and his judgments cannot be dismissed without serious attention paid to them.