Signalling by morphogens such as the Hedgehog family, Notch, Wingless/Wnt and various growth factors is essential during embryogenesis. The establishment of concentration gradients of these morphogens plays a key role during developmental patterning in all multicellular organisms, assuring that distinct cell/tissue types and organs appear at the right place in the right time during embryogenesis. Regulation of morphogen synthesis, trafficking and diffusion are all known to play a part in setting up these gradients, and a complex web of signaling mechanisms ensures that specific responses occur at the correct threshold concentration in the recipient cells whose fate depends on these morphogens.