Cell polarity and identity play important roles in the development of many organisms and the correct localisation of key proteins is vital for proper functioning of multicellular systems. mRNA localisation within the cell provides an important means of delivering proteins to their correct site of function within the cell cytoplasm. The importance of mRNA localisation was first shown two decades ago in Ascidian embryos, where the majority of β-Actin mRNA accumulates in the myoplasm. In chicken fibroblast cells Actin mRNA is localised to the leading edge of the cell, later shown to be essential for cell motility. Further studies include yeast and many multicellular organisms, such as Xenopus, protozoa, plants and Drosophila melanogaster. Drosophila development is regulated utilising asymmetric mRNA localisation on many levels and provides the first symmetry-breaking step in the development of the unfertilised egg. In recent years several examples have emerged of mRNA localisation by directed transport along microtubules or Actin using cytoskeletal motors. However, the details of the mechanisms of RNA movement have not been eluded fully. This thesis provides exciting new evidence for the mechanisms of mRNA localisation during Drosophila oogenesis and shows that the RNA encoding one key developmental regulator, grk mRNA uses multiple steps involving motor proteins which transport the cargo along ortholog populations of microtubules within the oocyte. Similar mechanisms of transcript localisation are likely to be utilised by many other key mRNAs during many stages of development and by diverse organisms.