The crystallnity index (CI) of cellulose has been commonly used as a parameter to assess/interpret cellulose structures in cellulosic plant biomass, after chemical, biological and/or enzymatic (cellulase) treatments. However, it has been found that the values of crystallinity index vary, depending on the choice of measurement method. With the increasing amount of research devoted to the preatreatment of lignocelluosic biomass for bioenergy production, this may have important implications in the assessment of pretreatment performance. Researchers from the National Renewable Energy Laboratory (NREL, United States) made critical comparisons of four different techniques incorporating X-ray diffraction (XRD) and solid state carbon-13 Nuclear Magnetic Resonance (NMR) methods, on eight different cellulose preparations. Results of the study point to the use of "caution against trying to correlate relatively small changes in the CI with changes in cellulose digestibility". Caution is advised due to the (1) complex nature of cellulase interactions with amorphous and crystalline cellulose, as well as (2) the possibility that factors other than crystallinity (such as lignin/hemicellulose content/distribution, porosity, particle size) may also affect accessibility of cellulose. The complete study is published in the open access journal, Biotechnology for Biofuels (URL above)..