Technical Abstract: The intent of this paper is to summarize data on 4,383 cows from several studies and to clarify synchronization of estrus or ovulation using GnRH and prostaglandin (PGF) with the Ovsynch, CO-Synch, and Select Synch protocols. The Ovsynch protocol resulted in higher (P<.05) pregnancy rates than Syncro-Mate-B (54% and 42%, respectively), but requires handling cows 4 times for injections and timed insemination. The CO- Synch protocol requires handling cows only 3 times, and results in similar (P>.1) pregnancy rates as the Ovsynch protocol to a timed insemination (54% and 58%, respectively). The addition of 48-hr calf removal between the PGF and 2nd GnRH injection facilitates animal handling and improves (P<.05) pregnancy rates to the Ovsynch and CO- Synch protocols approximately 8%. The Select Synch protocol differs from the Ovsynch and CO-Synch protocols in that it is used to synchronize estrus rather than ovulation. The Ovsynch, CO-Synch, and Select Synch protocols all resulted in similar (P>.1) pregnancy rates, and all were capable of inducing estrous cycles in anestrous cows. Combinations of the Select Synch with the CO-Synch protocol allow a producer to take advantage of high pregnancy rates to insemination after observation of estrus and utilize timed insemination among non-responding cows. However, delaying the 2nd injection of GnRH and timed insemination beyond 48 hr following the PGF injection appears to decrease pregnancy rates.