How many Bitcoin halvings have there been?

there have been three Bitcoin halving events. They occurred at block heights:

1. November 28, 2012 (First halving)
2. July 9, 2016 (Second halving)
3. May 11, 2020 (Third halving)

Each halving reduces the block reward miners receive for validating transactions on the Bitcoin network by half. The block reward started at 50 bitcoins per block and halved to 25 bitcoins after the first halving, then halved again to 12.5 bitcoins after the second halving, and finally halved to 6.25 bitcoins after the third halving.