The rise of two-dimensional (2D) materials and their heterostructures has revolutionized modern materials science. Understanding and manipulating charge transport in 2D materials and charge transfer (CT) across their interfaces play a paramount role in determining application performance. Employing time-resolved terahertz spectroscopy, this dissertation investigates interfacial CT in heterostructures and charge transport in 2D covalent organic frameworks (COFs). Following the pump-wavelength dependent CT mechanism at graphene-WS2 interfaces, we find that defects can rapidly trap injected or photogenerated electrons in WS2 within ~1 ps and store them beyond ~1 ns. This leads to long-lived charge separation and efficient photogating in graphene. Further electrochemical modulation of defect occupation in WS2 leads to a flip of the local photogating field, from electron-photogating in p-doped heterostructures to hole-photogating in n-doped heterostructures. In graphene-nanographene heterostructures, strong interlayer π-π interactions enable the ultrafast and efficient transfer of holes from nanographene to graphene, contributing to the excellent photodetection performance. Furthermore, the size of nanographene acts as a structural knob that regulates interfacial vdW interactions, thereby modifying the electronic coupling strength and CT efficiency. Finally, we unveil that crystallinity plays a critical role in determining the charge transport properties of 2D COFs. In highly crystalline 2D COF thin films, band-like transport prevails with record-high local charge mobility up to hundreds of cm2V–1s–1. Our findings elucidate charge transport and transfer effects in emerging 2D materials and their hybrids, providing new insights into the design and optimization of advanced electronic and optoelectronic devices.