Molecular signals are sensed by their respective receptors and information is transmitted and processed by a sophisticated intracellular network controlling various biological functions. Optogenetic tools allow the targeting of specific signaling nodes for a precise spatiotemporal control of downstream effects. These tools are based on photoreceptors such as phytochrome B (PhyB), cryptochrome 2, or light-oxygen-voltage-sensing domains that reversibly bind to specific interaction partners in a light-dependent manner. Fusions of a protein of interest to the photoreceptor or their interaction partners may enable the control of the protein function by light-mediated dimerization, a change of subcellular localization, or due to photocaging/-uncaging of effectors. In this review, we summarize the photoreceptors and the light-based mechanisms utilized for the modulation of signaling events in mammalian cells focusing on non-neuronal applications. We discuss in detail optogenetic tools and approaches applied to control signaling events mediated by second messengers, Rho GTPases and growth factor-triggered signaling cascades namely the RAS/RAF and phosphatidylinositol-3-kinase pathways. Applying the latest generation of optogenetic tools allows to control cell fate decisions such as proliferation and differentiation or to deliver therapeutic substances in a spatiotemporally controlled manner. Optogenetic tools enable the spatiotemporal control of the function of genetically encoded proteins by light. The authors discuss optogenetic tools and approaches applied to control signaling events mediated by second messengers, Rho GTPases and signaling cascades namely the RAS/RAF and PI3K/AKT pathways. Applying the latest generation of optogenetic tools allows to control cell fate decisions such as proliferation and differentiation or to deliver therapeutic substances in a spatiotemporally-controlled manner. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.