In November 2004, lesbian couple Katherine Zappone and Ann Louise Gilligan (K & AL) were granted leave by the High Court to pursue a claim to have their September 2003 Vancouver marriage recognised for the filing of joint tax returns in Ireland.

[1] Mr. Justice Liam McKechnie remarked that the case was significant and would embrace far-reaching issues touching many aspects of society.

Lead barrister, Gerard Hogan, argued that neither the 1937 Irish constitution nor more recent tax laws specifically define marriage as between one man and one woman.

[8] Ms. Justice Dunne found that although a "living document", the Constitution of Ireland had always meant for marriage to be between a man and a woman, that the definitions used in the Civil Registration Act of 2004 was an expression of the current attitudes of the state and that she could find no reason to change that.

[11] In 2008, the couple published a joint memoir, Our Lives Out Loud: In Pursuit of Justice and Equality, which detailed the background to the case.

Katherine Zappone and Ann Louse Gilligan renewed their marriage vows at a ceremony in Dublin City Hall on 22 January 2016.