Tamoxifen has persisted as a widely accepted and administered drug for almost 25 years. Following the many scientific papers and books on the subject, it has remained a very intriguing substance. This, perhaps, is the reason for another monograph on Tamoxifen. It is regrettably true that overviews, even when up to date after exhaustive research – the shibboleth of our cultures -, rapidly lose relevance with the passage of time. Scientists can sometimes be pictured as deep sea divers, who plunge into the unknown in search of a hitherto unknown world. Their descent is exciting, but eventually they must come up for air and integrate their experiences with others who also had to resurface. This book intends to collect and, where possible, to collate recent, but sometimes seemingly unrelated information. To quote Stephane Mallarme: "Everything in the world exists to end up in a book". Even if this is a tad cynical, it might not be far from the truth. If a little knowledge is a dangerous commodity, one can also add – tongue in cheek – that a vast amount of knowledge can be truly hazardous. It is likely that what might seem as entangled data is confusing, especially for those satisfied with the comfortable interpretation of Tamoxifen as an antiestrogen which has long been found insufficient. The complexity of its mechanisms and effects defies simple explanations and may even seem capricious, but only because of our ignorance.