Surface meteorological mesonetworks are becoming increasingly prevalent worldwide. The success of a network is ultimately dictated by the quality of its observations. Sensors with sufficient accuracy for standard networks are readily available and there are in many cases numerous sensors to choose from. Many factors need to be considered when selecting sites and the appropriate sensors for a network. Site accessibility and sensor cost, power consumption, accuracy, and durability are just a few factors to consider; manufacturer reliability, longevity, and customer service should not be overlooked. Note that a good sensor in one application is not necessarily the best choice in another. A high quality sensor, if used incorrectly or for the wrong application, can produce undesirable results. This talk discusses mesonetwork design and sensor selection with emphasis on observations relevant to the water cycle.