This review provides a comprehensive overview of the electronic properties of two-dimensional graphene, focusing on carrier transport in doped or gated graphene structures. It emphasizes the unique features of graphene's electronic properties, which arise from its gapless, massless, chiral Dirac spectrum. The review critically compares graphene's carrier transport with that of two-dimensional semiconductor systems, such as heterostructures, quantum wells, and inversion layers, to highlight the distinct characteristics of graphene. It discusses both experimental and theoretical aspects of quantum and semi-classical transport, aiming to provide a unified perspective. The review covers various physical mechanisms controlling transport, including long-range charged impurity scattering, screening, short-range defect scattering, phonon scattering, many-body effects, Klein tunneling, minimum conductivity at the Dirac point, electron-hole puddle formation, p-n junctions, localization, percolation, quantum-classical crossover, midgap states, quantum Hall effects, and other phenomena. The review begins with an introduction to the scope and background of graphene, including its structure, band dispersion, and electronic properties. It then discusses quantum transport, transport at high and low carrier densities, and quantum Hall effects. The review also addresses the intrinsic and extrinsic nature of graphene, highlighting the distinction between intrinsic and extrinsic graphene based on the presence of charge neutrality points and the ability to gate or dope the system. The review emphasizes the unique electronic properties of graphene, such as its linear energy-momentum dispersion, chiral nature, and the absence of a bandgap, which make it a distinct material compared to traditional 2D semiconductors. The review concludes with a summary of the key findings and highlights the importance of graphene's unique properties in the context of electronic materials science.This review provides a comprehensive overview of the electronic properties of two-dimensional graphene, focusing on carrier transport in doped or gated graphene structures. It emphasizes the unique features of graphene's electronic properties, which arise from its gapless, massless, chiral Dirac spectrum. The review critically compares graphene's carrier transport with that of two-dimensional semiconductor systems, such as heterostructures, quantum wells, and inversion layers, to highlight the distinct characteristics of graphene. It discusses both experimental and theoretical aspects of quantum and semi-classical transport, aiming to provide a unified perspective. The review covers various physical mechanisms controlling transport, including long-range charged impurity scattering, screening, short-range defect scattering, phonon scattering, many-body effects, Klein tunneling, minimum conductivity at the Dirac point, electron-hole puddle formation, p-n junctions, localization, percolation, quantum-classical crossover, midgap states, quantum Hall effects, and other phenomena. The review begins with an introduction to the scope and background of graphene, including its structure, band dispersion, and electronic properties. It then discusses quantum transport, transport at high and low carrier densities, and quantum Hall effects. The review also addresses the intrinsic and extrinsic nature of graphene, highlighting the distinction between intrinsic and extrinsic graphene based on the presence of charge neutrality points and the ability to gate or dope the system. The review emphasizes the unique electronic properties of graphene, such as its linear energy-momentum dispersion, chiral nature, and the absence of a bandgap, which make it a distinct material compared to traditional 2D semiconductors. The review concludes with a summary of the key findings and highlights the importance of graphene's unique properties in the context of electronic materials science.