This research focuses on the fundamental fluid mechanics of fountains. Attention is restricted to fountains formed by the vertical injection of fluid into a uniform environment of marginally differing density such that the momentum of the ejection is opposed by buoyancy. The small density dif- ference between the two miscible fluids permits dilution of the ejected fluid and, for sufficiently energetic ejections, turbulent entrainment occurs. Our experimental study of dense saline solution forced vertically upwards into a quiescent freshwater environment examines fountains arising over a broad range of source conditions. We combine experimental results with dimensional reasoning and theoretical arguments to provide meaningful and significant additions to the existing knowledge of fountain dynamics. The results presented enhance our understanding through the study of rise heights, the fluctuations in rise heights and the scale and balance of bulk fluxes within fountains over the range of source conditions. A study of transient and steady-state behaviours and associated fountain rise ratio (peak relative to mean rise heights) identifies previously unreported dynam- ics which extend published results - these include the pinch-off of the initial vortex and rise height ratios (unexpectedly) below unity. Analysis of the rise height fluctuations during the quasi-steady state provides characteristic length, time and velocity scales distinct to the varied classes of fountain flow. Our results for the rise height ratio and indeed rise height fluctuations reveal a number of differing classes of fountain behaviour; behaviour which highlights the changing and complex nature of fountains. This results in a consistent classification which extends the previous three classes of fountain behaviour to five. Some of the implications of these new behaviours to practical engineering and geophysical applications of fountains are discussed.