A handfasting ceremony is an ancient commitment ceremony that dates back to pre-Christian Celtic times in Ireland and Scotland. Today the ceremony is one type of marriage ceremony common among practitioners of Wicca and Neo-Paganism, which have their roots in the ancient Earth-based religion of the Celts. In the ceremony, a couple's wrists are tied together by a special cord or ribbon.

Under ancient Irish (Brehon) law, handfasting was one of many forms of marriage. Originally, it was what we today would call an engagement ritual, or trial marriage. A couple agreed to stay together for a year and a day, and at the end of the period, they would either decide to make the marriage permanent, agree to another temporary commitment or separate. The intent of the ceremony under Brehon law was to protect individual and property rights and official recognition of any children of the union.

There are many variations of the handfasting ceremony, and couples can design a handfasting ceremony according to their own desires. They exchange vows and usually rings, but it varies in other ways from traditional Christian marriage ceremonies. For example, instead of a bride wearing a white wedding gown, she often wears red, and the ceremony is performed in a circle. In the ceremony, the officiant ties the cord around the wrists of the couple, and if the cord is tied in a knot, it symbolizes the permanent status of the relationship. This is where the term "tying the knot" originates from.

The ceremony may or may not be legally binding, depending on whether the officiant is legally licensed to perform marriage ceremonies. Couples often pledge their marriage not "for as long as you both shall live," but "for as long as love shall last." One custom is that while facing each other, the couple places their right hands together and then their left hands, forming an infinity symbol while a cord is tied around their hands in a knot. In another custom, the man and woman place their right hands only together while a cord is used to tie a knot around their wrists.

The couple can choose the color of the handfasting ribbon or cord based on symbolism of the colors. Red is often chosen for its symbolism of passion, strength, fertility, courage, health, vigor and lust. Blue represents tranquility, understanding, patience, health, truth, devotion, sincerity, honor, loyalty, peace and wisdom. Black signifies empowerment, vision, success, pure love, unlocking when stuck and banishing evil or negativity. Pink stands for unity, honor, truth, romance, happiness, healing, familial or emotional love (rather than sexual), friendship, affection, unselfish emotions, spiritual healing and the absence of hatred.