Who can give a “get?”
A literal interpretation of Jewish law says that only a man may start religious divorce proceedings, and he must do so voluntarily. A man would generally have a sefer k’ritot (scroll of severance) written to end the marriage. Some Orthodox authorities still hold strictly to this law, but Conservative, Reform, and even many Orthodox authorities agree that the wife may begin the process of the get by convening a beit din (rabbinical court). However, a woman cannot give a get, and she cannot force her husband to give her a get against his will.
Who may need a "get?"
Any Jewish person who has been married to another Jew of the opposite sex is eligible to receive a get. If you are a Jewish person who married someone who is not Jewish or married someone of the same sex, you are not eligible to receive a get and do not need one to be considered divorced.
If you are a Jewish person who did not have a religious marriage or were married by an official of another religion (for example, in a Unitarian, Episcopal, Methodist, Baha’i, Buddhist, or Hindu ceremony), you are still eligible to receive a get if your spouse is Jewish by birth. This is because halacha (Jewish law) accepts a marriage as valid once it has been performed, even if it was made without signing a ketubah (Jewish marriage contract).
Why would someone need a "get?"
If a person was married to someone of the opposite sex under Jewish law, that person cannot remarry under Jewish law without a get. Without a get, s/he would still be considered married under Jewish law, even if s/he received a divorce under state law (civil law). Also, without a get, children from any future marriages would be considered mamzerim (illegitimate) under Jewish law. You can also read What are “mamzerim?” How are they treated within Jewish communities? for more information. However, a woman who gets divorced under state law (civil law) can still legally remarry under state law without a get from her former husband.
Many Reform rabbis are willing to perform a wedding for a person who only has a civil divorce from his or her former spouse, but it is necessary to get a get to remarry in the Orthodox and Conservative communities. Reform, Reconstructionist, and unaffiliated Jews may still feel they need a get in order to conform to the strictest interpretation of the law.
Many non-religious Jews choose to marry under a chuppah (wedding canopy), sign a ketubah (marriage contract), and have a Jewish wedding performed by a rabbi or cantor. However, many non-religious Jews in heterosexual marriages may not realize that in order to remarry under Jewish law, they need to obtain a halachic (Jewish law) divorce. If you are a non-religious, unaffiliated, Reform, or Reconstructionist Jew who married in a Jewish wedding ceremony, you may wish to get a get so that you can remarry under Jewish law and have that marriage recognized by all denominations (streams) of Judaism. However, if this is not important to you, you may decide you do not need to pursue a get.
Orthodox authorities hold that Jews who were married in civil ceremonies must also receive a get in order to be able to remarry under Jewish law. If you were married under civil law, you may still want to get a get to conform with a strict interpretation of the law.
Are there any proactive measures a woman can take to avoid becoming an “agunah” in case the marriage ends?
One of the best ways to prevent the possibility of becoming an agunah (“chained woman”) is to include a “Lieberman Clause” in either a prenuptial agreement or a ketubah (Jewish marriage contract). A Lieberman Clause is named for Rabbi Lieberman, the Reform rabbi who first introduced it. This clause says that in the event of divorce, the husband agrees to give a get and the wife agrees to accept it. You can learn more about including this kind of requirement in a prenuptial agreement on the Beth Din of America’s website The Prenup.
Many observant couples sign a prenuptial agreement agreeing to the terms of a future get. Increasingly Reform, Conservative, and modern Orthodox rabbis insist on the parties signing the prenup before officiating. Some of the Orthodox rabbinate argues that writing this kind of agreement into the ketubah is non-halachic (invalid under Jewish law), but many Orthodox rabbis would support writing this sort of clause into a prenuptial agreement. The Conservative rabbinate supports adding a Lieberman Clause into a ketubah or into a prenuptial agreement. A Jewish prenuptial agreement can be entirely separate from any secular (nonreligious) prenuptial agreement that the parties may or may not have, and can refer exclusively to the responsibility of both parties to give and accept a get should the need arise.
If a Lieberman Clause was not included in a ketubah or a prenuptial agreement, couples who are already married can sign a postnuptial agreement to include a Lieberman Clause. This may seem like an awkward step for a married couple to take. However, it is another way to safeguard both parties’ rights in the event of the marriage’s end.