Book excerpt: This book describes nitric oxide (NO) and hydrogen peroxide (H2O2) functions in higher plants. Much progress has been made in the field of NO and H2O2 research regarding the various mechanisms and functions of these two molecules, particularly regarding stress tolerance and signaling processes, but there are still gaps to be filled. NO and H2O2 are both crucial regulators of development, and act as signaling molecules at each step of the plant lifecycle, while also playing important roles in biotic and abiotic responses to environmental cues. The book summarizes key advances in the field of NO and H2O2 research, focusing on a range of processes including: signaling, metabolism, seed germination, development, sexual reproduction, fruit ripening, and defense.