Blood vessels deliver nutrients and oxygen to tissues. Importantly, the functions and growth of blood vessels are commonly altered in disease. The inside of all blood vessels are lined with endothelium, a thin specialized layer of endothelial cells that separate the blood from other tissues. This thesis deals with the identification and functional characterization of proteins and microRNAs that have key roles as modulators of growth factor signaling and directed cell migration of endothelial cells and other vascular cells. A previously uncharacterized protein of the exocyst complex, Exocyst complex component 3-like 2 (ExoC3L2) was identified and shown to be highly expressed in endothelial cells of sprouting vessels. Suppression of ExoC3L2 resulted in reduced VEGF-A signaling together with reduced chemotaxis in response to VEGF-A gradients. VEGF-A-signaling via its receptor VEGFR-2 is thus modulated by the exocyst complex and ExoC3L2. Expression profiling of highly vascularized tissues were used to identify several microRNAs selectively expressed in blood vessels. miR-145, targeting the transcription factor Fli1, was shown to be expressed in pericytes and mural cells. Elevated levels of miR-145 reduced chemotaxis of both endothelial cells and fibroblasts in response to growth factor gradients. miR-145 depletion in fibroblasts was shown to inhibit chemotaxis in response to PDGF-BB. The guanine nucleotide exchange factor FGD5 was shown to be selectively expressed in endothelial cells and to regulate Cdc42 activity. FGD5 was shown to regulate the turnover of activated VEGF-receptors. Suppression of FGD5 impaired endothelial cell chemotaxis, suggesting that FGD5 is required for efficient and sustained VEGF-A signaling. Inactivation of RhoD, a regulator of endosomal trafficking, resulted in an increased pool of acetylated and stable microtubules. Knockdown of RhoD in human fibroblasts resulted in a loss of cell polarity. A link between PDGFR-β and RhoD was implicated by the finding that PDGF-BB was shown to trigger formation of GTP-bound RhoD. Chemotaxis towards PDGF-BB was severely inhibited in cells with reduced RhoD expression, suggesting a role for RhoD in chemotaxis via its regulation of microtubule dynamics.