A serious consideration for those who want to know more about the inside aspect of ETs, the paranormal, Nazi UFOs, time travel, hybrids, and Mars and the Moon. And more. Easy to read, many facts given, and some pictures I have not seen in over 45 years of my research into the field. I had no questions about his findings since my research and info agreed with his, and I usually question mark whole sections of books like this. A very good starter on ET involvement in Earth affairs, second to Sitchin's works in significance. Get it and enjoy.
(Jaybo.  Review on Border's Books)

Ufology 201 - A survey course of the extraterrestrial scene September 13, 2011
An up-to-date overview of the literature with carefully and responsibly chosen sources. Secret in the sense that you won't these kinds of views (or almost any kind of ufology views) represented in the mass media. Not as enigmatic as Keel, or as deep as Marrs, but definitely a required read for a newbie who wants to get their feet wet in a hurry. Engaging and easy to read. His analyses help make sense of the complex terrain, motivations, personalities, background and diversity of the UFO scene. If you have been following the the ET scene closely for the last ten years you might not learn much, but if you haven't you will probably go to bed each night with your head swimming in disbelief at what you read. This is not to say that this work is overly controversial, just that the media blackout on this type of information is very effective. The author chooses key players and interviews them to bring himself up to speed. Then he uses that background to investigate and chart a meaningful course for the reader. He does not present himself as a field investigator or an expert, but as an intelligent interpreter. If an author cannot find accurate ufology information, it is because your tax dollars have been spent to disinform and hide, not because the author did not look for the answers. Lets you know, for example, that many so-called skeptics like Sagan, were actually doing contract work with government ET data that unequivocally demonstrated the opposite reality. Recommended, includes an 11 page chapter bibliography and index.
(A Reader. Review on 9/13/2011

“Len Kasten’s The Secret History of Extraterrestrials provides an indispensable key to unlocking the hidden history of the extraterrestrial presence on our planet. The scope and implications of Kasten’s book are breathtaking, not because of some sleight of hand by an ambitious author, but because of the greater reality he unveils of extraterrestrials historically interacting with humanity.? 
(Michael E. Salla, M.A., Ph.D., founder and president of Exopolitics Institute )

“With our present knowledge of the cosmos, there is now a real possibility of evolved and intelligent civilizations elsewhere in the vast cosmological space. And possible visitations and even encounters can no longer be ignored. Naturally we must tread with caution and not jump to conclusions too easily and too readily; but we must also keep an open mind and respect those bold investigators who apply rigorous research and common sense to this fascinating although very debated hypothesis. Len Kasten is such an investigator, and his book The Secret History of Extraterrestrials is a must for the libraries of all seekers of truth with unbiased minds.? 
(Robert Bauval, author of The Orion Mystery, Message of the Sphinx, and Black Genesis )

“Len Kasten has provided an up-to-date survey of the vast array of issues that are now emerging into the public consciousness regarding an extraterrestrial presence engaging the human race. For those who want to jump right into the pool and not just sit on the side and dangle their feet, take the plunge with The Secret History of Extraterrestrials.? 
(Stephen Bassett, executive director of Paradigm Research Group )

“This comprehensive book covers some of the most intriguing UFO and alien-contact cases ever reported. Len Kasten has done a fine job of drawing together some fascinating material and asks some profound questions about what this means for the human race.? 
(Nick Pope, UK Ministry of Defense, 1985-2006 )

“You can always count on Len Kasten to take you on a spellbinding galactic adventure, for he never fails to seek out ideas and theories that challenge your assumptions of what is true while firing your imagination. Whether in this dimension or another, be it past or future, your travels with Len Kasten will open your mind and introduce you to realities and experiences, you may have mistakenly assumed can exist only as fiction.? 
(Paul Davids, director/producer of Jesus in India and executive producer/cowriter of Roswell: The UFO Coverup )

I found Mr. Kasten’s The Secret History of Extraterrestrials well done and worthy of respect. I esteem Kasten’s rare ability to characterize the UFO phenomenon and history in all of its colors. He courteously declines a narrowly focused box of what’s safe from a materialistic point of view… probably because it’s not what he envisions for a truly full picture. He believes his audience is well read in the phenomenon and intelligent enough to appreciate the varying intricacies and questions he brings to light. He refreshingly avoids employing the need to persuade and puts it all out there for the reader to judge. He marries the scientific and the non-materialistic artfully, which takes us to the fertile realm of the Open Question once again. All of this he does without disparaging any one area of focus within the field of study. Without a doubt more cross pollinated leadership would enhance the collegial environment in the UFO field. Thank you, Mr. Kasten, for an intelligently presented, well researched gestalt view of the phenomenon.
(Tracey Lynn Buchanan, Colorado MUFON member)

"Len Kasten, in "The Secret History of Extraterrestrials," exposes information that has been withheld or covered up by government officials as well as underground information about Nazi ties to UFOs and their secret base in Antarctica. He also gives actual accounts of abductions, interbreeding with abductees, and speculation by visionaries. 

Personally, I did intensive study in the 1980s on extraterrestrials and can attest to having a few experiences similar to those in "The Secret History of Extraterrestrials." It was refreshing to me to re-visit this aspect of my life and contemplate on Kasten's research. I believe his research is valid and well thought out. However, since this is a controversial topic, those that are skeptical may want to read this book with an open mind. Those that do believe in another realm of beings will find that Kasten was able to pull together information and compile it in a concise, reader-friendly manner." 
(Irene Watson for Amazon Reader Views)