This book explores the essence of the institution of marriage: what is the meaning of marriage today, how has marriage been influenced by the legal recognition of new cohabitation models, and what should be the role of the institution of marriage in the future? In order to understand what marriage actually is in the 21st century, it is necessary to identify and analyze the formalities and function of marriage in society. With a focus on Sweden, the book examines the historical development of marriage - beginning as a 'gift from God' and now being a gender-neutral institution - from a legal and political perspective and taking into account the past and present role of the Church of Sweden. The book then makes comparative assessments concerning the legal and political developments leading toward the adoption of gender-neutral marriage concepts in the Netherlands and Spain despite different societal backgrounds. In addition, the significance of the marital status under European Union law is explored, under the Charter of Fundamental Rights of the European Union and in the jurisprudence of the European Court of Justice. Also, the relevant decisions based on the European Convention of Human Rights, as interpreted by the European Court of Human Rights, are examined. The book discovers that the key role that the institution of marriage has played in the past still influences the essence of marriage today and charges it with a special symbolic value.