This chapter examines the flexural and shear behavior of steel-concrete sandwich (SCS) composites consisting of slotted perforated plate connectors. An extensive laboratory program evaluates mechanical performance, critical failure mechanisms and the effect of key design parameters. The proposed snap-in connector enhances composite action via two complementary shear transfer mechanisms: (i) mechanical interlock of the slotted plates to resist transverse shear, and (ii) concrete tenons formed within the perforations to prevent vertical separation of the steel plates. It provides a practical alternative to traditional designs such as overlapping studs and J-hook, and effectively minimizes interfacial slip. Under pure bending, the beams exhibit near-perfect composite action with minimal bond-slip and a characteristic flexural failure involving sequential yielding of the tension steel followed by concrete crushing. Under shear, resistance is provided jointly by the concrete tenons and connector action along diagonal sections. Beams with ultra-high performance concrete (UHPC) cores achieve markedly higher capacity and deformation tolerance, attributable to fiber-bridging and post-cracking toughness that strengthen the concrete tenons. Mechanics-based analytical models are developed for flexural and shear resistance, capturing elastic-plastic stress distribution at normal sections and the combined tenon-connector mechanism at shear-critical sections.