Peptides encoded by small open reading frames (sORFs, usually <100 codons) play critical regulatory roles in plant development and environmental responses. Despite their importance, only a small number of these peptides have been identified and characterized. Genomic studies have revealed that many plant genomes contain thousands of possible sORFs, which could potentially encode small peptides. The challenge is to distinguish translated sORFs from nontranslated ones. Here, we highlight advances in methodologies for identifying these hidden sORFs in plant genomes, including ribosome profiling and proteomics. We also examine the evidence for new peptides arising from sORFs and discuss their functions in plant development, environmental responses, and translational control.