Studies from the past 6 years have demonstrated how estrus events and intensity are associated with ovulation, ovarian and uterine function, and fertility. Data from recent studies involving spontaneous and induced estrus have shown that greater relative increase and longer duration of estrus, captured by different activity monitors, significantly improve pregnancy/AI (around 10 to 15% units across different studies) and decrease pregnancy losses. Intensity and duration of estrus were surprisingly only weakly associated with follicle diameter and concentration of estradiol at estrus. The likelihood of ovulation was greater for estrus episodes with high vs. low relative increase in physical activity. Data from 2 studies showed that estrus behavior near AI also modified the expression of genes related to the immune system, adhesion molecules and prostaglandin synthesis in the endometrium and those related to apoptosis, progesterone synthesis and prostaglandin receptor in the corpus luteum. Most recently, studies from the United States and Canada demonstrated that reproductive programs using activity monitors and emphasizing detection of estrus can be successful and comparable to intensive timed AI protocol-based programs. One last study from our laboratory also concluded that the inclusion of GnRH at AI greatly improved P/AI from cows bred upon estrus events, but only those of low intensity, which showed the potential to use activity monitors as a tool in targeted protocols. Quantitative information from estrus events could be used to improve estrous detection quality and develop decision-making strategies at the farm level. Further studies in this field should aim to (1) better understand ovarian, embryo and endometrium mechanisms associated with either the expression or intensity of estrus and, 2) refine the collection of phenotypes related to estrus (i.e., relative increase, absolute increase, baseline levels, duration, and repeatability within cow) to improve estrous detection and possibly genetic selection.