Lipopolysaccharide (LPS) is a major Virulence determinant of the human bacterial pathogen Hoemophilus influenzae. A characteristic feature of H. influenzae LPS is the extensive intra- and inter-strain heterogeneity of glycoform structure which is key to the role of the molecule in both commensal and disease-causing behaviour of the bacterium. The chemical composition of non-typeable Haemophilus influenzae (NTHi) LPS is hi-lily diverse. It contains a number of different monosaccharides (Neu5Ac, L-glycero-D-manno heptose, D-glycero-D-manno heptose, Kdo, D-Glc, D-Gal, D-GlcNAc, D-GaINAc) and non-carbohydrate substituents. Prominent non-carbohydrate components are O-acetyl groups, glycine and phosphates. We now know that sialic acid (N-acetylneuraminic acid or Neu5Ac) and certain oligosaccharide extensions are important in the pathogenesis of NTHi: however, the biological implications for many of the various features are Still unknown. Electrospray ionization mass spectrometry ill combination with separation techniques like CE and HPLC is an indispensable tool in profiling glycoform populations ill heterogeneous LPS samples. Mass Spectrometry is characterized by its extreme sensitivity. Trace amounts of glycoforms expressing important Virulence determinants can be detected and characterized on minute amounts of material. The present review focuses oil LPS structures and mass spectrometric methods which enable us to profile these in complex mixtures.