This paper is mostly a review of the progress made at NIST in pursuing a capacitance standard based on the charge of the electron. We briefly introduce the Coulomb blockade, which is the basic physical phenomenon allowing control of single electrons, describe two types of single- electron tunnelling (SET) device and describe the metrology goals and payoffs achievable from SET devices. We then discuss the electron-counting capacitance standard (ECCS): the motivation, previous experimental work on various critical elements, present status and future prospects. This last part includes using the ECCS for a practical representation of capacitance, as well as pointing out that we can close the quantum metrology triangle without needing a large-value current standard. Finally, we briefly review other SET-based metrological applications.