Hans Holzer's career was a unique whirl wind of books, research, lectures, teaching, hundreds of national and regional talk show appearances, co-hosting/hosting programs such as Ghost Hunter on Boston's Channel 2, NBC's In Search Of with Leonard Nemoy (an Alan Landsburg production), Beyond The Five Senses in Louisville, KY, Explorations with Brownville Productions in Ohio. In radio, he had a continuous segment with New York City's WOR station with famed radio personality Joe Franklin who still remains a family friend. Some books and case work yielded films such as Amityville II: The Possession, the adaptation from his best-selling novel Murder in Amityville, based on his work on the case in Amityville, Long Island and The Amityville Curse, which also became a film in 1989 that went to Sweden, the US in 1990 and then in 1991, was released in Japan.

Holzer became and still is considered a leading authority in the field of the paranormal, having earned his PhD from the London College of Applied Science. He spent over six decades traveling the world to obtain first-hand accounts of paranormal experiences, interviewing expert researchers, and developing para-psychological protocols and terminology such as 'sensitive' and 'beings of light.' He taught a class in parapsychology at the New York Institute of Technology for nearly a decade.

One of his favorite quotes comes from T.S. Elliot's Confidential Clerk saying blandly, "I don't believe in facts." Hans did. "Facts,", he said, "come to think of it—are the only things—I really do believe in."

This book, Exploration of the Unknown, features excerpts from many of his published works, the first section dealing with hauntings and supernatural investigations, and the second section dealing more with his philosophical, biographical, and metaphysical works. All of the books excerpted are available in eBook format (and some in digital audio) from Crossroad Press as part of "The Essential Hans Holzer Collection."