This thesis describes a variety of local magnetic measurements performedusing scanning Superconducting QUantum Interference Device (SQUID) mi- croscopy to probe both fundamental material properties of superconductors as well as functional superconducting devices. We present an experimental study of the family of superconductors AV3Sb5 (A = Cs, K, Rb), based on a Kagome lattice. In particular, we probe the temper- ature dependent superconducting penetration depth of these three compounds and find that all three show a finite superconducting gap throughout the Fermi surface. This work is described in a manuscript published in Physical Review Materials (Kaczmarek, Phys. Rev. Materials 9, 074802, (2025)), and here we in- clude some additional data and analysis. Next, we discuss a series of measurements in functional superconducting de- vices: transition edge sensors (TESs). Large detector arrays of TESs are used in astronomy telescopes, making possible incredibly precise cosmology measure- ments including that of the cosmic microwave background. In particular, we use scanning SQUID microscopy to directly image the superconducting prox- imity effect in these devices as a function of temperature and bias, and observe competing effects of the direct and inverse proximity effect from nearby su- perconducting and metal structures respectively. Additionally, we explore the spatial evolution of the bias current through these devices, which we can cor- relate directly to the local superconducting and normal regions of the device. Finally, we present measurements of the devices in magnetic field. This work is described in a series of published manuscripts: IEEE Trans. Appl. Supercond. 35, 1 (2025).; arXiv:2602.19399; and a paper on the current imaging is in prep. Finally, we discuss our measurements on a different kind of functional su- perconducting device used for sensing: kinetic inductance detectors (KIDs), a type of photon detector based on a superconducting resonator circuit. In partic- ular, we directly image the vortex configuration in different parts of the device, and correlate changes in the resonance of these RF devices with the presence of vortices.