In this talk, I will discuss our recent work in developing novel electronic and photonic devices based on the emerging two-dimensional (2D) materials. I will first present our work in understanding the fundamental electronic and optical properties of low-symmetry 2D materials such as black phosphorus (BP) using a newly developed scanning ultrafast electron microscopy (SUEM) technique. Our recent study of bandgap tuning in BP and the demonstration of BP based optical detectors will also be presented. In the second half of my talk, I will discuss our work on developing an atomically-thin resistive memory device based on two-dimensional materials that demonstrates record low current/power operation with promising potential applications in ultra low power computation and memory.