Sturge–Weber Syndrome (SWS) is a rare congenital disorder presenting with a vascular malformation in the upper face and brain, causing impaired blood–brain barrier function and perfusion, increased calcium signaling, inflammation, and seizures. All these neuropathologic processes result in injury to the brain. The somatic GNAQ R183Q variant, which accounts for the majority of SWS cases, increases signaling through MAPK, PI3K, mTOR, and inflammatory pathways, primarily in endothelial cells. The discovery of this variant enabled the creation of transgenic and genetic animal and cell culture models. Generating in vitro models has been challenging due to the mosaic nature of SWS, and attempts to separate unaffected from mutant cells in primary culture have failed, limiting the utility of in vitro work. Ongoing in vitro work seeks to overcome these limitations, shape our understanding of SWS, and lead to translational advances in treatment and prevention by studying the affected molecular pathways and identifying future targets for therapy.