Metal ion separation and preconcentration constitute the pivotal step in numerous analytical, purification, and waste treatment processes. Increasing environmental regulations and growing economic incentives imply that separation science will be essential to the future of industrial processing. This volume offers a broad perspective of advances in the field while also including up-to-date work in a number of specialized areas. It begins with an overview which describes the objectives the book, summarizes each chapter, and presents some immediate challenges for the future. Two review chapters then address the status of metal ion separations in nuclear energy and defense-related programs. These are followed by twenty chapters covering a range of topics, including aqueous phases in separations, extractant design and synthesis, solvent extraction, solid-liquid distribution, separations using membranes, centrifugal partition and countercurrent chromatography, and supercritical fluid extraction systems. Together the essays provide a fine balance of fundamental and applied research, making the book invaluable for both novice and experienced practitioners.