In California, there are two grounds for divorce (also known as dissolution):

Irreconcilable differences, this is the most common basis for seeking a divorce. The court will require no further explanation. It is not necessary to establish that either spouse had any "fault" in the breakdown of the marriage.

Incurable insanity (rarely used). The spouse seeking the divorce must provide medical proof that the other spouse was insane when the petition was filed — and will remain incurably insane.

In addition, one spouse must have lived in California for six months and in their county for three months before filing a petition to dissolve the marriage.

There is no residency requirement for filing a petition for legal separation.