Polyamine (PA) metabolism and functions have started to gain the attention of plant scientists in the last few years. In plant organisms, the most common biogenic amines (spermine, spermidine and putrescine) are known primarily for their ability to mitigate the negative effects of biotic and abiotic stresses on plants and are involved in a number of various processes that ensure proper cell function. Plant PAs have been recognized for their roles as membrane, protein and nucleic acid stabilizers, as protectors of cellular integrity and photosynthetic machinery, as direct and indirect signaling agents, and as emerging members of the non-enzymatic antioxidant system. Currently, the knowledge of the role of PAs in many developmental and morphogenetic processes occurring in plants can be extended by interfering with PA biosynthesis pathways with appropriate inhibitors, the availability of PA mutants, and molecular biology methods. The accumulation of PAs in response to many abiotic and biotic stresses is one of the most remarkable plant metabolic responses. This chapter provides an overview of available data on PA functions in plants, synthesis, catabolism and involvement in plant cell responses to drought, salinity, low and high temperatures and biotic stressors.