Deprivation of liberty refers to "any form of detention or imprisonment or the placement of a person in a public or private custodial setting which that person is not permitted to leave at will by order of any judicial, administrative or other authority" [1]. Under international human rights law, a person may be considered deprived of their liberty even where the state does not characterise their detention as such, in situations where the state instigates, consents to or acquiesces in the deprivation [2]. Deprivation of liberty extends well beyond formal arrest or imprisonment and encompasses a wide range of situations, including police custody, pre-trial and administrative detention, immigration detention, house arrest, confinement in transit or border zones, and informal detention by state or non-state armed actors [3].

In conflict settings, deprivation of liberty also encompasses confinement in unofficial sites including private homes, military facilities and makeshift detention centres [4]. Arbitrary detention is prohibited and the obligation to ensure humane treatment of those detained applies regardless of the identity of the detaining party or the formal characterisation of the situation [5]. This prohibition is grounded in both international human rights law – primarily Article 9 of the International Covenant on Civil and Political Rights (ICCPR), which provides that "everyone has the right to liberty and security of person" and that "no one shall be subjected to arbitrary arrest or detention" – and customary international humanitarian law applicable in both international and non-international armed conflict [6]. Unlawful confinement of civilians constitutes a grave breach of the Fourth Geneva Convention and a crime under the Rome Statute of the International Criminal Court ("Rome Statute") [7]. The United Nations (UN) Standard Minimum Rules for the Treatment of Prisoners ("Nelson Mandela Rules") and the Body of Principles for the Protection of All Persons under Any Form of Detention or Imprisonment (1988) elaborate the minimum standards of treatment to which all persons deprived of their liberty are entitled [8].

Persons deprived of their liberty are among those most acutely vulnerable to sexual and gender-based violence (SGBV). Across the full spectrum of deprivation of liberty, from formal detention facilities to unofficial sites, immigration detention, and situations of control over freedom of movement, the power imbalance between those exercising control and those deprived of liberty, creates conditions of extreme vulnerability [9]. Individuals deprived of liberty are wholly dependent on those who control their access to food, water, medical care, communication and release, a dependence that can be exploited to facilitate exploitation and abuse. SGBV is often normalised or dismissed as "collateral damage" and enabled by this power imbalance [10]. It is used as a tool of interrogation, punishment, humiliation, coercion and political repression [11].

While all persons deprived of their liberty face heightened risk, forms of SGBV experienced differ significantly across groups. Women and girls face particular risks of rape and sexual slavery, as documented across conflict settings from Bosnia to Sudan to Gaza [12]. Men and boys face distinct and extensively under-reported forms of sexual violence including rape, genital violence and sexual humiliation, often deployed specifically to attack masculinity and provoke shame [13]. SGBV is systematically under-reported due to severe barriers to disclosure including fear of reprisal, shame, lack of access to legal counsel, absence of independent complaint mechanisms and profound distrust of the very authorities responsible for detention [14].