This review considers the development and application of hydrodynamic ultramicroelectrodes (H-UMEs). These electrochemical systems comprise an amperometric UME, with a characteristic dimension on the micrometre or sub-micrometre scale, operated in a well-defined convective- diffusive regime. The greatly enhanced mass-transport rates that can be attained quantitatively at H-UMEs, over a wide dynamic range, has considerable benefits in terms of measuring fast kinetics and in analytical applications. Four types of H-UMEs are assessed: (i) fast-flow tubular and channel microelectrodes; (ii) a dropping mercury microelectrode; (iii) a microscopic wall-tube electrode, termed the microjet electrode (MJE); and (iv) a radial flow micro-ring electrode (RFMRE). Hydrodynamic modulation methods are also described, that can be used in association with UMEs to extend amperometric detection limits. Finally, possible future directions for H-UMEs are considered briefly, along with new methods for enhancing the timescale of dynamic electrochemical measurements.