Nanofluidics, a field emerging from microfluidics, explores fluid transport at the nanometer scale. This review discusses the unique phenomena and mechanisms at these scales, emphasizing the interplay between bulk and interface effects. It highlights the validity of continuum approaches, surface-induced effects like hydrodynamic slippage and electro-kinetic phenomena, and the importance of nanoscale length scales. The review also explores the role of surface chemistry in optimizing fluid properties and the challenges in achieving molecular-scale confinement. Key length scales, including the molecular scale, Bjerrum length, Debye length, and slip length, are discussed, along with their implications for fluid transport. The review concludes that while Navier-Stokes equations remain valid for water in nanochannels down to ~1 nm, achieving molecular-scale confinement remains a technological challenge. Surface effects, such as slip and electro-kinetic phenomena, play a crucial role in nanofluidic applications, offering opportunities for technological breakthroughs in filtration, desalination, and energy conversion. The review emphasizes the importance of understanding these length scales and their interactions to advance nanofluidics.Nanofluidics, a field emerging from microfluidics, explores fluid transport at the nanometer scale. This review discusses the unique phenomena and mechanisms at these scales, emphasizing the interplay between bulk and interface effects. It highlights the validity of continuum approaches, surface-induced effects like hydrodynamic slippage and electro-kinetic phenomena, and the importance of nanoscale length scales. The review also explores the role of surface chemistry in optimizing fluid properties and the challenges in achieving molecular-scale confinement. Key length scales, including the molecular scale, Bjerrum length, Debye length, and slip length, are discussed, along with their implications for fluid transport. The review concludes that while Navier-Stokes equations remain valid for water in nanochannels down to ~1 nm, achieving molecular-scale confinement remains a technological challenge. Surface effects, such as slip and electro-kinetic phenomena, play a crucial role in nanofluidic applications, offering opportunities for technological breakthroughs in filtration, desalination, and energy conversion. The review emphasizes the importance of understanding these length scales and their interactions to advance nanofluidics.