Prior to ovulation, cows display certain behaviors that we characterize as estrous behavior. The standing reflex, a behavior that by definition accompanies heat, is important for determining the moment of insemination. These animals, which are ovulating, can then be inseminated with success. Only 50% of the cows display this standing reflex, however, so it is necessary to formulate a better and more conclusive definition of estrus. An effective and valid visual detection scoring system has been developed. With this system, the intensity of estrous behavior can be expressed numerically both for individual cows and at the herd level. Other ways of detecting cows in estrus are discussed, such as using pedometers, body temperature, electrical conductivity and heat mount detectors. Most of the aids that have been developed are not reliable or sensitive enough to relieve the farmer from frequent visual observation of the herd. Pedometers and heat mount detection devices seem to be the most promising detection aids.