Eukaryotic cells express numerous ArfGAPs (ADP-ribosylation factor GTPase-activating proteins). There is increasing knowledge about the function of the brain-specific protein ADAP1 [ArfGAP with dual pleckstrin homology (PH) domain] as well as about its biochemical properties. The ADAP subfamily, also designated centaurin-α, has an N-terminal ArfGAP domain followed by two PH domains. The mammalian ADAP subfamily consists of two identified isoforms, ADAP1 and ADAP2 (centaurin-α1 and -α2). ADAP1 is highly expressed in neurons. We highlight the functional roles of ADAP1 in neuronal differentiation and neurodegeneration. Because of interactions with different proteins and phosphoinositol-lipids, ADAP1 can function as a scaffolding protein in several signal transduction pathways. Firstly, ADAP1 mediates cytoskeletal crosstalk. This is indicated by multiple interactions of ADAP1 with components of the actin and microtubule cytoskeleton. Secondly, regulation of neuronal polarity formation and axon specification by ADAP1 is suggested by crystal structural data obtained for human ADAP1, and the complexes of ADAP1-Ins(1,3,4,5)P4 and/or the forkhead-associated domain of the kinesin KIF13B. These structures support the concept that a KIF13B-ADAP1 complex enhances the local accumulation of PtdIns(3,4,5)P3 at the tips of neurites, and thus favors neuronal polarity. Thirdly, recent evidence unravels a pathological role of ADAP1 because upregulation of ADAP1 by amyloid β-peptide causes ADAP1-Ras-ERK-dependent translocation of Elk-1 to mitochondria. This impairs mitochondrial functions with subsequent synaptic dysfunction and exacerbates neurodegeneration, as in Alzheimer's disease.