Mistletoe was originally part of the old Druidic religion. Pagans in Britain used the plant in religious ceremonies and rites, especially at the Winter Solstice on December 21st.
This plant is parasitic and it lives on apple and willow trees. The ancient Britains hung it around the house to protect against evil spirits. It also symbolised friendship which is why we associate it today with kissing.
MISTLETOE IN AN APPLE TREE

When Christianity first came to Western Europe, mistletoe (and holly) was banned from churches and considered anti-Christian, but in some places the tradition of holding "Mistletoe Service" in churches continued and was merged into the Christian tradition. York Minster Cathedral was one place where such services were held. Wrongdoers could attend the service and leave the cathedral pardoned.
Kissing under the mistletoe is an old English custom that is now observed all over the world. Traditionally, the person being kissed picked a mistletoe berry for every time they were kissed and once the berries had been picked there could be no more kisses.
MISTLETOE BERRIES

So, if you like this tradition, get yourself some mistletoe with lots of berries.
CAUTION: Mistletoe can be harmful to cats, dogs and children. Take care if the berries start to fall off.