Two‐dimensional (2D) materials of atomic thickness have emerged as nano‐building blocks to develop high‐performance separation membranes that feature unique nanopores and/or nanochannels. These 2D‐material membranes exhibit extraordinary permeation properties, opening a new avenue to ultra‐fast and highly selective membranes for water and gas separation. Summarized in this Minireview are the latest ground‐breaking studies in 2D‐material membranes as nanosheet and laminar membranes, with a focus on starting materials, nanostructures, and transport properties. Challenges and future directions of 2D‐material membranes for wide implementation are discussed briefly. Separation goes small: Two‐dimensional materials of atomic thickness have emerged as high‐performance separation membranes. The latest advances in the design and fabrication of 2D‐material membranes are reviewed, along with a discussion about the challenges for future applications.