The establishment of neuronal morphology is essential for the formation of the nervous system. In general, neurons undergo a developmental programme during which their immature processes are specified into one axon and several dendrites. Extension of axons and dendrites is then critical for the establishment of appropriate connectivity. A body of work implicates the PI3K (phosphoinositide 3-kinase) signalling pathway to be crucial during the various events leading to the formation of neuronal circuit. In this review, we will focus specifically on the function of PI3K and downstream signalling cascades that control the establishment of axonal specification and elongation.