The terms ‘cohabitation’ or ‘cohabitation relationship’ in their broadest meaning comprise all forms of relationships between two persons (ie including marriage), but normally they are used to describe non-marital relationships. In principle, this therefore includes all other types of formalized unions, eg the Dutch geregistreerd partnerschap, the French pacte civile de solidarité (PACS) and New Zealand’s civil unions. If interpreted more narrowly, ‘cohabitation’ does not include formalized unions for same-sex couples (same-sex relationships), which are the functional equivalent of marriage. Examples include the registered partnership in some of the Nordic countries, civil partnership in the United Kingdom, the German Eingetragene Lebenspartnerschaft or Eingetragene Partnerschaft in Austria or Switzerland. This entry will focus on cohabitation in this narrower sense, ie couple relationships other than those in a marriage or a functional (but formalized) equivalent.
In addition to ‘cohabitation’, many other terms are used to describe non-marital relationships (particularly those which have not been entered into through a formal act, see below), such as de facto unions, common law marriage (common law) etc. These terms often suggest that these relationships function similarly to a marriage and perhaps should even be treated the same in law. But this might be inappropriate, especially for those couples who consciously decided not to enter into a marriage (or similar legal regime).
Historically, non-marital unions were often classified as ‘concubinage’ (concubinatus), although, depending on the socio-historical context, this might refer to a relationship which was an alternative to marriage or to an extra-marital relationship of a person already married to someone else, or, as in some cases, merely a lesser form of marriage. For a long time, concubinage was a perfectly acceptable or at least a tolerated form of social and family life, but in 1563 the Council of Trent (Concilium Tridentinum) outlawed such unions in the so-called Tametsi decree.
The quotation Les concubins ignorent la loi, la loi ignore donc les concubins (sometimes also quoted as Les concubins se passent de la loi, la loi se désinteresse d’eux) is generally attributed to Napoléon, and indeed that sentiment used to reflect the legal view on cohabitation in most jurisdictions (and in some that is still true today). Yet even Napoléon’s Code civil,in Arts 515-8, today contains a legal definition of concubinage as a de facto union of two persons of the same or opposite sex living together as a couple in a stable, enduring relationship. As there is no further limitation, this means that a concubinage is possible even when one of the parties involved is married to another person. The Swedish Sambolag (2003:376) (Act on Cohabitants), in § 1, defines sambor (cohabitants) as ‘two persons, living in an enduring couple relationship and having a joint household’. Yet in Sweden, as in the majority of European jurisdictions (but not in France or, according to the reform proposals, in England and Wales), the application of the legal rules for cohabitants is expressly precluded if one of the parties is married to another person. Likewise, the rules on prohibited degrees of marriage are often applicable to cohabitation relationships, or similar rules have been implemented. However, the Belgian registered partnership (wettelijke samenwoning/cohabitation légale), which merely requires a joint written declaration to the competent public registrar, can be entered into by any two persons, so that, for example, father and son can become registered partners. Hence, in Belgium a registered partnership is deliberately conceptualized to include non-conjugal relationships, eg caring relationships.
2. Social development and practical relevance
The actual practical relevance of cohabitation seems to follow a societal development having roughly three phases. In the first phase, cohabitation is very rare (and often secret) and is perceived by the majority as deviation from the norm and ‘sinful’ or ‘wrong’; the consequences of cohabiting with another range from social ostracism to severe criminal (or ecclesiastical) sanctions. In the next phase, cohabitation is more common and, if not accepted, then at least tolerated, particularly as a prequel to or a ‘test-phase’ for marriage; still, marriage remains the family form considered appropriate and promoted by the majority, particularly if the couple have children. In the third and final phase, cohabitation and marriage are both equally accepted forms of living together.
This development can be discerned in almost all European jurisdictions in one fashion or another, with most European jurisdictions currently in the second phase. Yet there appears to be something of a north-south divide. In the Nordic countries, Scotland, France and some eastern European countries like Slovenia and Croatia, the development has begun earlier, and cohabitation is accepted socially and subject to comprehensive legal rules. The central European countries (including Germany, Austria and Switzerland) and England and Wales are in an intermediate position. Southern European jurisdictions are the slowest and currently in the beginning stages of such a development, although in some of the autonomous communities of Spain, legal rules for cohabitants have been in place for quite some time. Still, in all European jurisdictions there has been a general increase in cohabitation relationships (albeit to varying degrees), and more and more children are born out of wedlock. For example, in the Nordic countries, the United Kingdom, France and Slovenia, between 40 and 50 per cent of children are born outside of marriage. This of course has led to cohabitation-specific legal problems which have required and will continue to require consideration.
3. Legal development
The increase in cohabitation relationships has inevitably brought with it an increase in the number and relevance of social and legal conflicts between and concerning cohabitants. Inevitably these issues have reached the courts, and in many European jurisdictions statutory provisions were soon implemented for specific issues concerning cohabitants. Typically, this first legal ‘recognition’ of cohabitants occurred in public law and especially in social welfare legislation, and was actually to the detriment of the cohabiting couple: eg social welfare benefits would be lower if a person lived in an enduring cohabitation relationship, as the relationship for the purpose of social welfare legislation was treated like a marriage. Likewise, a divorcee receiving maintenance would often suffer a reduction (or even termination) of the maintenance payments if cohabiting with a new partner. In this early phase of legal recognition of cohabitation, legislation regarding leases and tenancies was also often amended (or interpreted differently) to make it possible for a cohabitant to remain in the joint dwelling upon the other’s (the tenant’s) death or in case of separation (see eg § 563(2) Bürgerliches Gesetzbuch (BGB) or for England, ss 36 and 38 Family Law Act of 1996 and Sch 1 to the Rent Act of 1977).
In the absence of express legal rules on cohabitation, the courts had to revert to the general law (see eg for Germany BGH 9 July 2008, FamRZ 2008, 1822, 1828 and Stack v Dowden  UKHL 17 for England and Wales). Unsurprisingly, the general law often was (and still is) not suited to deal with the specific legal problems of cohabitants and this led to (and in many jurisdictions still leads to) what can be perceived as unfair outcomes, disadvantaging the financially or socially weaker cohabitant and also (indirectly) the children of that relationship (subject to whatever financial remedies might exist in law for their benefit).
In response to this, several European legislatures have decided to adopt a coherent legal framework for cohabitants. Two basic approaches can be discerned. The first (see a) below) requires the couple to formalize their relationship in some manner (eg by signing a contract or registering with a public authority) in order to be subject to the legal regime. This is the approach taken by the French pacte civile de solidarité (PACS) and many other legal regimes generally referred to as ‘registered partnerships’ (but see the section on definitions above and same-sex relationships) as in the Netherlands, Andorra, Luxembourg and some of the autonomous communities in Spain. The second approach (see b) below) is not to require a formal act, but rather to rely on the existence of certain facts, eg a certain period of living together or having joint children; this is the case, for example, in Sweden, Portugal, Scotland, Croatia and Slovenia. In some jurisdictions (particularly some of the autonomous communities in Spain), a hybrid or compromise between the two approaches exists, so that the legal regime applies either if the couple have registered or, in the absence of such a registration, after a certain time of having lived together and/or having parented a joint child. This has the advantage that the couple can opt into the legal regime right from the start if they so wish and do not have to wait until the stipulated period of living together has passed.
a) Formalized or formal cohabitation
In those jurisdictions where the legislature has made a formal act a requirement for the application of the statutory provisions on cohabitation (eg Arts 515 ff French Code civil; Arts 1475 ff Belgian Civil Code; Arts 80a ff Burgerlijk Wetboek (BW)), the underlying concept emphasizes the private autonomy of the parties over the protection of the weaker party: without the express agreement of both parties the legal regime will not apply.
Where formal cohabitation regimes exist, they are generally open to both same-sex and opposite-sex couples, as often the legislature sought to address two issues with one stroke of the pen, namely giving cohabitants a legal framework and, often for the first time ever, giving same-sex couples the opportunity to formalize their relationship and give it legal recognition (same-sex relationships). However, this is somewhat problematic as it offers one solution for two groups who might have very different interests: couples who cannot marry (because they are of the same sex) and couples who do not want to marry. The underlying motives for entering into a legal regime, the parties’ expectations and the legal desiderata therefore are quite likely to be different. In addition, it can be argued that this approach perpetuates rather than diminishes discrimination because same-sex couples under this approach only have access to one way of formalizing their relationship, whereas opposite-sex couples can choose between formalized cohabitation and marriage. These considerations have led jurisdictions like the Netherlands and Belgium to open up marriage to same-sex couples as a second step after first introducing a legal regime of formalized cohabitation.
The substantive rules for formalized cohabitation regimes are quite different from each other. At one end of the spectrum is the Netherlands, where the geregistreerd partnerschap has more or less the same legal consequences of marriage (with some exceptions, particularly as to dissolution). By contrast, the French pacte civil de solidarité (PACS) is a legal regime very distinct from marriage and of much lesser legal impact. At the other end of the spectrum there is the Belgian wettelijke samenwoning/cohabitation légale, with comparatively few legal consequences in private law, but more far-reaching ones in tax and social welfare and social security law.
Finally, it is apparent that in all jurisdictions that have introduced a regime of formalized cohabitation, there is still a need to deal with the legal problems arising out of informal or de facto cohabitation: in all these jurisdictions, we find not only court decisions but also specific and selective statutory rules (rather than a coherent regime) in certain areas of law addressing legal issues surrounding cohabitation. It is evident that a regime of formalized cohabitation cannot deal with the problems of all cohabiting couples; it merely adds another ‘intermediate level’ of legal rules between marriage (and, where available, the functional equivalent for same-sex couples) and informal/de facto cohabitation.
b) Informal or de facto cohabitation
In jurisdictions where the legal rules applying to cohabitants are dependent on certain facts being fulfilled rather than a formal act, the legislature appears to have given priority to the protection of the weaker party (and the children) over the autonomy of the parties: the legal rules apply irrespective of an express agreement and potentially against the wishes of at least one party. However, the private autonomy of the couples is actually protected because in almost all jurisdictions the couple is free to expressly opt out of the legal regime should they so desire.
The factual requirements of the regime usually include having lived as a couple for a specified period of time, such as two or five years, or for a ‘longer period of time’. The latter designation is used where the legislature felt a defined cut-off date was inappropriate. In some jurisdictions, the period of living together is dispensed with if the couple have joint children; other jurisdictions—like Scotland—do not have a minimum duration requirement.
The legal consequences of informal or de facto cohabitation vary significantly from jurisdiction to jurisdiction, even where an express regime has been introduced. In some jurisdictions—like Croatia and Slovenia—the legal consequences are modelled on or are similar to those of marriage; in others—like Sweden, Scotland and the Republic of Ireland (and in the reform proposals for England and Wales)—the statutory rules are deliberately and distinctively different from those of marriage.
4. ECJ, ECtHR and cohabitation
The ECJ has on several occasions had the opportunity to adjudicate on the legal differentiation between marriage and cohabitation, namely in cases where cohabitants claimed benefits afforded only to married couples (see eg ECJ Case C-59/85 – The Netherlands v Reed  ECR 1283). In these decisions, the ECJ has always interpreted the term ‘marriage’ autonomously and held that there was neither a European legal requirement to treat married and cohabiting couples equally nor was it possible to interpret the term ‘spouse’ to include an unmarried cohabitant.
Similarly, the ECtHR considers marriage and mere de facto relationships to be distinct and allows the national legislature a wide margin of appreciation on whether legal remedies and benefits available to married couples must be extended to cohabitants (see eg Mata Estevez v Spain, No 56501/00; Burden v United Kingdom, No 13378/05; Courten v United Kingdom, No 4479/06; Schalk and Kopf v Austria, No 30141/ 04).
5. Convention no 32 of the Commission Internationale de l’État Civil and recognition of foreign cohabitation regimes
The Commission Internationale de l’État Civil (CIEC) (International Commission on Civil Status), on 5 September 2007, adopted a Convention on the recognition of registered partnerships (Convention (no 32) sur la reconnaissance des partenariats enregistrés). The Convention has so far only been signed by Spain and Portugal and has only been ratified Spain. The Convention in many ways is a minimum compromise, and the legal rules in place in many jurisdictions already have a much wider scope and application than the Convention. The Convention only applies to registered, ie formalized, relationships and thus not to informal or de facto cohabitation.
Yet a general recognition of foreign family law regimes other than marriage (including both formalized and de facto cohabitation) is needed urgently, particularly since the legal regimes available in the various jurisdictions have very different legal consequences. The current state of the law is a significant impediment to the free movement of workers in the European Union. Only when family law regimes entered into or applicable in one jurisdiction are recognized when a couple moves to another jurisdiction can it be said that the worker can choose his workplace freely, without the fear of losing rights and duties held under a currently applicable family law regime. In 2011 the European Commission therefore put forward a proposal for a Council regulation on jurisdiction, applicable law and the recognition and enforcement of decisions regarding the property consequences of registered partnerships (COM(2011) 127/2) which at least would deal with the private international law issues for formalized cohabitation relationships.
6. Future development
The increasing number of cohabitation relationships puts the national legislatures under pressure to address and legislate on this social development and provide adequate legal solutions for very real and existing problems. Where reforms are being contemplated, there is a clear tendency to recognize informal or de facto cohabitation relationships and not to make recognition contingent on a formal act.
In all European jurisdictions, part of the debate focuses on whether and how the legal recognition of cohabitation relationships might endanger the institution of marriage. However, in those jurisdictions that have legislated on cohabitation, there seems to be little evidence of an adverse effect on marriage. In any event, it is to be expected that the common European development, with increasing numbers of cohabiting couples and children born in these relationships, ie the social reality of modern family life, will lead sooner or later to the implementation of legal rules for cohabitation relationships in all European jurisdictions.
Justitiedepartementet, Statens offentliga utredningar (SOU) 1999:104—Nya samboregler (1999); Kathleen Kiernan, ‘The Rise of Cohabitation and Childbearing Outside Marriage in Western Europe’ (2001) 1 IJLPF 1; Wendy Schrama, De niethuwelijkse samenleving in het Nederlandse en het Duitse recht (2004); Cristina González Beilfuss, Parejas de hecho y matrimonios del mismo sexo en la Unión Europea (2004); Jens M Scherpe and Nadjma Yassari (eds), Die Rechtsstellung nichtehelicher Lebensgemeinschaften—The Legal Status of Cohabitants (2005); Anne Barlow, Simon Duncan, Grace James and Alison Park, Cohabitation, Marriage and the Law—Social Change and Legal Reform in the 21st Century (2005); Herbert Grziwotz, Nichteheliche Lebensgemeinschaft (4th edn, 2006); Law Reform Commission (Ireland), ‘Report—Rights and Duties of Cohabitants’ (LRC 82-2006); Law Commission (England and Wales), ‘Cohabitation: The Financial Consequences of Relationship Breakdown’ (Consultation Paper no 179, 2006; Law Com no 307 CM 7182, 2007); Inge Kroppenberg and others (eds), Rechtsregeln für nichteheliches Zusammenleben (Beiträge zum europäischen Familienrecht, vol 12, 2009).