The responses of wells to changes in atmospheric pressure (barometric effects) are briefly reviewed. Barometric effects can arise in both confined and unconfined aquifers. The basic requirements are: (1) the presence of an aquifer with some rigidity and (2) material above the saturated aquifer with low pneumatic diffusivity to prevent changes in atmospheric pressure being transmitted quickly and directly to the water table. In addition, the well must be cased to the top of the saturated aquifer and be in reasonable hydraulic connection with it. In confined aquifers, measuring barometric efficiency can provide a simple way of estimating storage coefficient. Barometric effects can be monitored with either vented or non-vented pressure transducers; neither type will eliminate barometric fluctuations and both need independent monitoring of changes in air pressure so that the barometric efficiency can be determined and the fluctuations removed from aquifer-test and similar data.