Ultrafast molecular separation (UMS) membranes are highly selective towards active organic molecules such as antibiotics, amino acids and proteins that are 0.5-5 nm wide while lacking a phase transition and requiring a low energy input to achieve high speed separation. These advantages are the keys for deploying UMS membranes in a plethora of industries, including petrochemical, food, pharmaceutical, and water treatment industries, especially for dilute system separations. Most recently, advanced nanotechnology and cutting-edge nanomaterials have been combined with membrane separation technologies to generate tremendous potential for accelerating the development of UMS membranes. It is therefore critical to update the broader scientific community on the important advances in this exciting, interdisciplinary field. This review emphasizes the unique separation capabilities of UMS membranes, theories underpinning UMS membranes, traditional polymeric materials and nanomaterials emerging on the horizon for advanced UMS membrane fabrication and technical applications to address the existing knowledge gap. This work includes detailed discussions regarding existing challenges, as well as perspectives on this promising field.