Methyl lactate [CH(CH 3)OHC(¼O)OCH 3 ] conformational space was investigated by extensive DFT/B3LYP/6-311þþG(d,p) and MP2/6-31þþG(d,p) calculations and matrix-isolation FTIR spectroscopy in argon and xenon matrices. From the seven different conformers predicted by the calculations, two forms (the most stable conformers yielded by the calculations: SsC and GskC, where the letters refer to the conformations assumed by the HOCC, OCC¼O and O¼COC dihedrals, respectively) were observed and characterized spectroscopically. Conformer interconversion pathways were also theoretically investigated. The low calculated barrier associated with the G 0 sk 0 C ! GskC conversion ($1 kJ mol À1) explains the absence of the third most stable form (G 0 sk 0 C) of methyl lactate in low-temperature matrices. Deposition of methyl lactate at different temperatures, together with the theoretical data, aided to the full assignment of the observed spectra. #