Thirty-four Populus biotechnology chapters, written by 85 authors, are comprised in 5 sections: 1) in vitro culture (micropropagation, somatic embryogenesis, protoplasts, somaclonal variation, and germplasm preservation); 2) transformation and foreign gene expression; 3) molecular biology (molecular/genetic characterization); 4) biotic and abiotic resistance (disease, insect, and pollution); and 5) biotechnological applications (wood properties, flowering, phytoremediation, breeding, commercialization, economics, and bioethics).