This review provides a comprehensive overview of the fundamental electronic properties of two-dimensional (2D) graphene, with a focus on carrier transport in doped or gated graphene structures. It highlights the unique features of graphene's electronic properties, which arise from its gapless, massless, chiral Dirac spectrum, by comparing it with 2D semiconductor systems such as heterostructures, quantum wells, and inversion layers. The review discusses both experimental and theoretical aspects of quantum and semi-classical transport, emphasizing the key mechanisms controlling transport, including long-range disorder, impurity scattering, screening, short-range disorder, 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, and quantum Hall effects. The scope of the review is limited to aspects of graphene transport where consensus exists in the literature, while also discussing open questions and active research topics. The review covers the basic physics of carrier transport in graphene, focusing on scattering mechanisms and conceptual issues, and provides a detailed discussion of the implications of graphene's linear energy-momentum relationship and chiral pseudospin quantum number. It also explores the differences between 2D graphene and 2D semiconductor systems, including their bandgaps, chirality, energy dispersions, and carrier confinement. The review concludes with a discussion of intrinsic and extrinsic graphene, emphasizing the importance of the charge neutrality point (CNP) and the ability to tune carrier density and type using external gating.This review provides a comprehensive overview of the fundamental electronic properties of two-dimensional (2D) graphene, with a focus on carrier transport in doped or gated graphene structures. It highlights the unique features of graphene's electronic properties, which arise from its gapless, massless, chiral Dirac spectrum, by comparing it with 2D semiconductor systems such as heterostructures, quantum wells, and inversion layers. The review discusses both experimental and theoretical aspects of quantum and semi-classical transport, emphasizing the key mechanisms controlling transport, including long-range disorder, impurity scattering, screening, short-range disorder, 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, and quantum Hall effects. The scope of the review is limited to aspects of graphene transport where consensus exists in the literature, while also discussing open questions and active research topics. The review covers the basic physics of carrier transport in graphene, focusing on scattering mechanisms and conceptual issues, and provides a detailed discussion of the implications of graphene's linear energy-momentum relationship and chiral pseudospin quantum number. It also explores the differences between 2D graphene and 2D semiconductor systems, including their bandgaps, chirality, energy dispersions, and carrier confinement. The review concludes with a discussion of intrinsic and extrinsic graphene, emphasizing the importance of the charge neutrality point (CNP) and the ability to tune carrier density and type using external gating.