Vegetarian eggs are eggs which come from hens who are fed a vegetarian diet. There are several different styles of these eggs, and many people associate them with the humane and ethical husbandry of chickens. These eggs are usually clearly marked at the grocers', and they may be more expensive than conventional eggs. Some people feel that this cost is worth it.
Interest in vegetarian eggs arose in response to concerns about chickens eating animal byproducts, including remains of other chickens. Since cannibalism has been linked with Transmissible Spongiform Encephalopathies (TSEs) in many species, some people expressed concerns that chickens which ate chickens could develop such a disease, potentially passing it on to people who ate them. Concern about eating chicken byproducts is also related to the natural repugnance which many people feel when they think about cannibalism, as the practice often seems wrong to people.
Ovo-vegetarians also like to seek out vegetarian eggs, especially ovo-vegetarians who pursue a vegetarian lifestyle out of concern for animal welfare. These consumers like the thought of eating eggs which come from a vegetarian chicken, and they also support the idea of raising chickens humanely. Other fans of humane animal raising practices may seek out vegetarian free range eggs to support this type of animal husbandry.
Practices used when raising vegetarian eggs vary. Many companies which sell them claim to raise free-range chickens, which means that their eggs are not actually vegetarian, since chickens are omnivores, and they will happily eat insects, worms, and other small creatures. However, the chicken farmers who raise free range chickens often sell their eggs as vegetarian anyway when their provided feed includes no animal byproducts.
Vegetarian eggs can also come from battery hens, however, so if animal welfare is a concern, you may want to find eggs which are certified as coming from free range chickens. The free range standards also vary widely, which is something to keep in mind. For example, chickens can be kept indoors for much of their life and still be considered “free range” as long as a door is periodically opened to theoretically allow the chickens out. When raised in these conditions, it is very easy to control the diet of the confined chickens, so ironically the only truly vegetarian eggs come from chickens who are not raised humanely, and are therefore dependent on the farmer for all their food.