Most chicken eggs produced for consumption are unfertilized. Eggs found in the grocery stores are typically produced by chickens that never come in contact with a rooster. In backyard flocks, however, there is usually a rooster present with the hens and he ensures that the eggs are fertilized by mating the hens regularly. Eggs from hens who have been mated in the past week are fertilized chicken eggs. They can be eaten or incubated and hatched into chicks. Yes, hens can and do lay unfertilized eggs. In fact, most grocery store eggs come from hens that have not been mated by a rooster and therefore are unfertilized. Yes, a hen that has not mated with a rooster in the past ten days will lay only unfertilized eggs. A hen that has never been with a rooster will only lay unfertilized eggs. A rooster must mate a hen for her to lay eggs, and after she is first mated it will still take about a week for her eggs to be fertilized, as it takes about that long for the roosters sperm to travel to the hens ovaries where her eggs are fertilized before the shell covers them and before they are laid.