In this thesis we employ highly surface specific vibrational sum-frequency generation (VSFG) spectroscopy to study neat liquid water and other, more complex aqueous interfaces. We focus in particular on hydrophobe/water interfaces to study the structure of water in contact with hydrophobic molecules. VSFG forms an ideal technique to study hydrophobe/water interfaces. With most other spectroscopic techniques the signal is dominated by the bulk, which implies that water-hydrophobe interactions can only be studied using amphiphilic molecules (for example alcohols) containing both hydrophobic and hydrophilic groups (to make them soluble in water). With VSFG it is possible to probe the interface of water and a layer of hydrophobic molecules with extremely high surface specificity. We thus study the properties of water near a layer of oil. We also investigate the surfaces of aqueous solutions of hydrophobic ions, and biologically relevant molecules like proteins and amino-acids.