The article is organized as follows. We first survey the computational studies on the interaction between engineered NTs and cell membranes. For NTs to be useful in a biological setting, they must remain stable in a cell membrane, which is composed of two hydrophilic outer layers separated by the inner hydrophobic core. We next highlight some of the groundbreaking experimental and computational work on water-conducting, ion-rejecting pores. These devices have obvious uses for water purification and desalination, as well as potential biological applications. Finally, we review some of the recent investigations on nanopores that are selectively permeable to either positively or negatively charged particles. It is of theoretical as well as practical interest to explore how a simple nanodevice made from one or two atomic species can mimic some of the functions of complex biological ion channels made of bulky membrane proteins.