Spring is the season of rebirth and renewal. Plants return to life after winter dormancy and many animals mate and procreate. Many pagan cultures held spring festivals to celebrate this renewal of life and promote fertility. One of these festivals was in honor of Eostre or Eastre, the goddess of dawn, spring and fertility near and dear to the hearts of the pagans in Northern Europe. Eostre was closely linked to the hare and the egg, both symbols of fertility.
As Christianity spread, it was common for missionaries to practice some good salesmanship by placing pagan ideas and rituals within the context of the Christian faith and turning pagan festivals into Christian holidays (e.g. Christmas). The Eostre festival occurred around the same time as the Christians’ celebration of Christ’s resurrection, so the two celebrations became one, and with the kind of blending that was going on among the cultures, it would seem only natural that the pagans would bring the hare and egg images with them into their new faith (the hare later became the more common rabbit).
The pagans hung on to the rabbit and eventually it became a part of Christian celebration. We don’t know exactly when, but it’s first mentioned in German writings from the 1600s. The Germans converted the pagan rabbit image into Oschter Haws, a rabbit that was believed to lay a nest of colored eggs as gifts for good children. (A poll of my Twitter followers reveals that 81% of the people who replied believe the Easter Bunny to be male, based mostly on depictions where it’s wearing a bowtie. The male pregnancy and egg-laying mammal aspects are either side effects of trying to lump the rabbit and egg symbols together, or rabbits were just more awesome back then.)
Oschter Haws came to America with Pennsylvania Dutch settlers in the 1700s, and evolved into the Easter Bunny as it became entrenched in American culture. Over time the bunny started bringing chocolate and toys in addition to eggs (the chocolate rabbit began with the Germans, too, when they started making Oschter Haws pastries in the 1800s).