The functional importance of carbohydrates in biological processes, particularly those involving specific molecular recognition, is immense. Characterizing the three-dimensional structures of carbohydrates and glycoconjugates and their interactions with other molecules, particularly the ubiquitous solvent, water, are key starting points on the road towards the understanding of these processes. The review introduces a new strategy, combining electronic and vibrational spectroscopy of mass-selected carbohydrate molecules and their hydrated (and also protonated) complexes, conducted under molecular beam conditions, with ab initio computation. Its early successes have revealed a uniquely powerful means of characterizing carbohydrate conformations and hydrated structures, the hydrogen-bonded networks they support (or which support them) and the specificity of their interactions with other molecules. The new information, obtained in the gas phase, complements that provided by more ‘traditional’ condensed phase methods such as NMR, X-ray diffraction, molecular mechanics and molecular dynamics calculations. The review concludes with a vision of the challenges and opportunities offered by applications of molecular beam spectroscopy and their relevance in a biological context. Contents PAGE 1. Preamble 490 2. Sweetness and light: Sugars in the gas phase 492 3. Experimental and computational strategies 495 4. The conformational landscapes of some key monosaccharides: glucose, galactose, mannose, fucose and xylose 498 4.1. Notation 498 4.2. Glucose, galactose and mannose 499 4.3. Fucose and xylose 503 5. Probing the glycosidic linkage: lactose and glycan ‘building blocks’ 504 5.1. Notation 506 5.2. Lactose 506 5.3. Mannose disaccharides 508 6. Adding water to sugar: hydrogen-bonding, co-operativity and selectivity 512 6.1. Notation 512 6.2. Mono-hydrated complexes: glucose, galactose and mannose 512 6.3. Co-operativity and conformational selectivity 516 6.4. Mono-hydrated complexes: xylose and fucose 519 6.5. Some concluding remarks 521 7. Using sugars: imino sugars and peptide mimics 522 7.1. Sugar mimics: imino sugars 522 7.2. Mimicking peptide secondary structure: carbopeptoids 524 8. Challenges and opportunities 527 Acknowledgements 529 References 530