This volume provides in depth reviews of the protein targeting translocation processes, gene transfer processes and genome reduction processes in the host and in the endosymbiont which were likely utilized during the evolution of an endosymbiont into mitochondria, mitochondria related organelles, simple and complex chloroplasts. These reviews cover both the current understanding of the host processes as well as the evolutionary outcomes used by these organelles for protein targeting and translocation. Reviews of the current knowledge of these topics are plentiful but scattered throughout the bacterial, parasite, plant and animal literature; here, reviews of current knowledge with evolutionary outcomes and future perspectives, written by leading researchers in their respective areas, are united into one comprehensive volume, essential for students and scientists interested in or working on subcellular protein localization, protein targeting signals, translocation of proteins across and insertion into membranes, nucleic acid transfer between genomes, genome reduction and evolution of mitochondria and chloroplast. .