An agunah is a married woman who for whatsoever reason is separated from her husband and cannot remarry, either because she cannot obtain a divorce from him or because it is unknown whether he is still alive. The term is also applied to a yevamah ("a levirate widow), if she cannot obtain ḥaliẓah from the levir or if it is unknown whether he is still alive (Git. 26b, 33a; Yev. 94a; and Posekim). The problem of the agunah is one of the most complex in halakhic discussions and is treated in great detail in halakhic literature (no less than six volumes of Oẓar ha-Posekim are devoted to it – see bibliography). The halakhah prescribes that a marriage can only be dissolved by divorce or the death of either spouse. According to Jewish law, divorce is effected not by decree of the court, but by thePage 511 parties themselves, i.e., by the husband's delivery of a get ("bill of divorce") to his wife. Hence the absence of the husband or his willful refusal to deliver the get precludes any possibility of a divorce. Similarly the mere disappearance of the husband, where there is no proof of his death, is not sufficient for a declaration by the court to the effect that a wife is a widow and her marriage thus dissolved. The husband, on the other hand, is unaffected by aginut, i.e., by his wife's refusal to accept the get or her disappearance without trace, since in such a case under certain conditions the law affords him the possibility of receiving hetter nissu'in ("permission to contract an additional marriage"). In most cases of agunot the question is whether or not the husband is still alive. Such cases result, for instance, from uncertainty about the husband's fate caused by conditions of war or persecution – particularly in recent times as a result of the Nazi Holocaust, but the problem can also arise, for example, if the husband suffers from chronic mental illness making him legally incapable of giving a get or simply if he willfully refuses to do so. Rabbinical scholars have permitted many relaxations in the general laws of evidence in order to relieve the hardships suffered by the agunah. On the other hand great care was always taken to avoid the risk that permission may inadvertently be given for a married woman to contract a second marriage that would be adulterous and result in any children from such a second marriage being mamzerim. Achieving both these ends, i.e., to enable the agunah to remarry while ensuring that an adulterous union does not result, is the object of intensive discussion in the laws of the agunah.