Higher plants typically do not produce trehalose in large amounts, but their genome sequences reveal large families of putative trehalose metabolism enzymes. An important regulatory role in plant growth and development is also emerging for the metabolic intermediate trehalose-6-P (T6P). Here, we present an update on Arabidopsis trehalose metabolism and a resource for further detailed analyses. In addition, we provide evidence that Arabidopsis encodes a single trehalose-6-P synthase (TPS) next to a family of catalytically inactive TPS-like proteins that might fulfill specific regulatory functions in actively growing tissues.