Urea occurs in nature and serves as a rapidly available nitrogen (N) source for the growth of many organisms, including pl-ants. This review gives a brief overview of the fundamental physiological significance of urea occurrence and its permeable proteins in various living systems. Mechanisms for urea generation and degradation in plants are discussed, and physiolo-gical roles of urea in plant N nutrition, metabolism and transport are highlighted. Two types of plant membrane transporters, namely MIPs and DUR3, potentially play roles in low- and high-affinity urea transport, respectively. MIPs mediate passive urea movement and were primarily investigated in heterologous gene-expression systems; AtDUR3 was shown to particip-ate in urea uptake in Arabidopsis roots. Transport characteristics, transcriptional regulation, and the subcellular localization of MIPs and DUR3 suggest the relevance of urea transport through these transporters in N nutrition and redistribution in planta.