Molecular Mechanisms of Axonal Growth -- Netrins and Their receptors -- Eph Receptors and Ephrin Ligands in Axon Guidance -- Role of Semaphorins during Axon Growth and Guidance -- Slits and Their Receptors -- Neurotrophic Factors: Are They Axon Guidance Molecules? -- The Role of Cell Adhesion Molecules in Axon Growth and Guidance -- Neurotransmitters and the Development of Neuronal Circuits -- The Hedgehog, TGF-?/BMP and Wnt Families of Morphogens in Axon Guidance -- The Role of Cyclic Nucleotides in Axon Guidance -- Membrane Lipid Rafts and Their Role in Axon Guidance -- The Role of Glial Cells in Axon Guidance, Fasciculation and Targeting. The complexarchitectureofneuronal networks togetherwith the extraordinary associated functions make the nervous system a fascinating biological structure. The considerable work performed to explore this cellular machinery is nowadays successfulbecause the mysteryofnervous system developmentisbeing unravelled. As described in their outstanding review published 10 years ago in Science.' Marc Tessier-Lavigne and Corey Goodman-the pioneers of the molecular era of axon guidance-summarized the assembly of nervous system connections as a subtle game of attraction and repulsion of neuronal growth cones. The cellular ballet ensuring the formation of billions of synapses, which ultimately gives rise to the highest cognitive functions, is primarily orchestrated by a step-by-step mechanism of growth driven by multiple molecular cues. While our general concept of axon guidance remains identical, a profound evolution ofour knowledge ofthe molecular identityofthe guidance cues together with their interactions and signalling pathways occurred over the past ten years. This book proposes an exhaustive and updated view ofthe current knowledge ofthe molecular and cellular mechanisms ensuring axon growth and guidance. An introductory chapterby C. Bouquetand F.Nothias will remind the readers ofall the features ofa growth cone and the mechanisms controlling its growth. From there, one enters a fabulous journey with a growth cone, a Tom Thumb story filled with molecular encounters and complex interactions leading to one ofthe most fantastic developmental achievements: the nervous system wiring.