No one can control, manage, or sustain what is not measured, so monitoring is the first step needed to ensure success. In terms of groundwater, monitoring can identify aquifers being used in an unsustainable manner and that information can then be used to find remedies to sustain the systems, as well as the industries and businesses that rely on them. One example of this, which will be discussed in this lecture, is the deep sandstone aquifer of northern Illinois and southeastern Wisconsin, where decades of overpumping have created one of the largest cones of depression in the world. Both states have conducted detailed studies of the aquifer and have begun regional planning to control the human and environmental impacts. (The McEllhiney Lecture Series is made possible by a grant from Franklin Electric.)