Conventional mooring systems in use today are mainly derived from technology that was developed from the 1950s through the 1970s. The subsurface or “intermediate” mooring design that matured in the 1970s allows measurements to be made reliably for up to 2 years. Thousands of these moorings have been deployed throughout the world's oceans and most marginal seas. A partial archive of the data that have been collected is available at http://ortelius.whoi.edu/website/BGTS/viewer.htm. Much of what we have learned about ocean circulation, and the processes governing it, has been provided by the world-wide effort to acquire moored (Eulerian) measurements of temperature, velocity, and other associated time series.