About 10 years ago, a new family of cell wall-deficient, iron-oxidizing archaea, Ferroplasmaceae, within the large archaeal phylum Euryarchaeota, was described. In this minireview, I summarize the research progress achieved since then and report on the current status of taxonomy, biogeography, physiological diversity, biochemistry, and other research areas involving this exciting group of acidophilic archaea.Microorganisms thrive remarkably under various conditions, including high temperatures, extremely high osmosis, and very acidic pH, that would generally be considered hostile or limiting to higher organisms. Studying and understanding the uniqueness of extremophilic organisms and the biochemical and cellular processes underlying their functioning and role in biogeochemical processes comprise an emerging research area in modern bioscience. Of special interest for various biotechnological applications are enzymes produced by extremophiles, the so-called extremozymes, which exhibit a high activity and stability under extreme physical-chemical conditions. The representatives of the "third domain of life," the archaea, are unique contributors to this area of special interest. Several factors make the archaea an attractive subject of study, including their relatively recent history of discovery, ability (often much higher than that of bacteria) to adapt to harsh environments, enigmatic nature, and low cultivability.