The Apparent Paradox of ROSAs aerobic organisms, plants live in an oxygen rich environment. Inevitable, reactive oxygen species (ROS) by-products and their chemical reactions are part of their basic metabolism. Initially documented as a toxic consequence of aerobic metabolism, ROS can also work as signaling molecules regulating crucial developmental and physiological events in many different organisms. Plants, animals, and even fungi have evolved mechanisms in which ROS are used as messengers to fulfill an extensive range of key biological processes. In Drosophila melanogaster, a signaling role for ROS was demonstrated in the differentiation of common myeloid progenitors in hematopoietic cells. Previously considered as toxic by-products of aerobic metabolism, reactive oxygen species (ROS) are emerging as essential signaling molecules in eukaryotes. Recent evidence showed that maintenance of ROS homeostasis during female gametophyte development is crucial for embryo sac patterning and fertilization. Although ROS are exclusively detected in the central cell of mature embryo sacs, the study of mutants deficient in ROS homeostasis suggests that controlled oxidative bursts might take place earlier during gametophyte development. Also, a ROS burst that depends on pollination takes place inside the embryo sac. This oxidative response might be required for pollen tube growth arrest and for sperm cell release. in this mini-review, we will focus on new insights into the role of ROS during female gametophyte development and fertilization. Special focus will be made on the mitochondrial Mn-Superoxide dismutase (MSD1), which has been recently reported to be essential for maintaining ROS homeostasis during embryo sac formation.