Conceptual models of hydrogeologic systems and solutions to practical problems were developed in the 18th century England to address serious water problems of national significance. Much of the learning was self-taught, and those who learned hydrogeology on their own passed it on to others by word of mouth. Eventually, hydrogeologic principles were documented in books and even newspapers. The first lecture in hydrogeology may have been given by William Smith in the early 19th century. About 140 years later, the first degree program dealing with groundwater hydrology was offered at the University of Arizona. Since then, substantial growth in the hydrogeology field has occurred in the US in response to federal regulations of the 1970s and 1980s dealing with water quality. The regulations led to increasing student applications, more universities offering programs in hydrogeology, and increased research support. With no new regulatory drivers and diminished perceived imminent threats to human health and the environment in recent years, the field of hydrogeology appears to have matured. An enormous amount of information, new technology, and new analytical tools have overwhelmed regulators and the regulated community. Although there appear to be many areas yet to explore, some of the more theoretical developments may be perceived by end users as having limited practical value or little immediate impact to solve existing problems. A key challenge is to put current theory and state of the art technology into practice.