The chapter details medical image registration and medical image fusion. The medical image registration deals with the introduction of a generic medical image registration scheme based on global transformations. This scheme consists of the identification of common features in the images to be registered, the definition of geometrical transformation, and the selection of an appropriate measure of match (MOM) between the reference and transformed image. It also includes the application of various optimization techniques for the determination of the transformation parameters with respect to the MOM. Qualitative and quantitative results are presented for registering computed tomography (CT)-magnetic resonance (MR) human heads (3-D case) using four well-known registration algorithms and their performances in terms of registration accuracy are also compared. The medical image fusion deals with the introduction of various techniques commonly used to combine information from different modalities, after the application of the medical image registration process.