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There are 3 main ways to end a marriage or registered domestic partnership in California: divorce, legal separation, and annulment. It is not necessary for both spouses or domestic partners to agree to end the marriage. Either spouse or partner can decide to end the marriage, and the other spouse/partner, even if he or she does not want to get a divorce, cannot stop the process by refusing to participate in the case. If a spouse or domestic partner does not participate in the divorce case, the other spouse/partner will still be able to get a “default” judgment and the divorce will go through.
California is a “no fault” divorce state, which means that the spouse or domestic partner that is asking for the divorce does not have to prove that the other spouse or domestic partner did something wrong. To get a no fault divorce, 1 spouse or domestic partner has to state that the couple cannot get along. Legally, this is called "irreconcilable differences".
After you decide how you want to end your marriage or domestic partnership, you need to plan your case ahead of time. Think about how you are going to handle your case. Planning before you start and talking to a lawyer can save you time and money as you go through the court process. And keep in mind that, normally, it does not matter who is the first to file the divorce or separation case. The court does not give any preference to the first person to file or a disadvantage to the person who responds to the case.
This excerpt is from the official California Courts website.