Metal ion release from metallic materials, e.g. metallic alloys and pure metals, implanted into the human body in dental and orthopedic surgery are becoming a major cause for concern. This book briefly provides an overview of both metallic alloys and pure metals used in implant materials in dental and orthopedic surgery. Additionally, a short section is dedicated to important biomaterials and their corrosive behavior in both real solutions and various types of media that model human biological fluids and tissues. The present book gives an overview of analytical methods, techniques and different approaches applied to measurement of in vivo trace metals released into body fluids and tissues from patients carrying metal-on-metal prosthesis and metal dental implants. Reference levels of ion concentrations in body fluids and tissues that have been determined by a host of studies are compiled, reviewed and presented in this paper. Finally, a collection of published clinical data on in vivo released trace metals from metallic medical implants is included.