Myo-inositol is essential in many cellular processes including membrane formation, cell-wall biogenesis, stress response and signal transduction. L-myo-inositol-1-phosphate synthase (MIPS) is the principal enzyme for its biosynthesis. The enzyme has been isolated and characterized from a number of systems including bacteria, protozoa, plants and animals. In this book, isolation and characterization of the enzyme has been presented from one important group, the pteridophyte, which has so far been left out. This work reports the MIPS activity and its partial purification from a fern, Diplopterygium glaucum (Thunb.) Nakai. Existence of two forms of MIPS in D. Glaucum in the cytosol and the chloroplast and differential thermotolerance between the two has also been described here.