Clarifying the causes of divorce, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada , states:

There are genuine cases when divorce is the only option available. Here are a few valid reasons:
1. Physical, mental, or emotional abuse or torture. When one of the spouses becomes abusive and inflicts physical, mental, or emotional torture, and is not willing to change by taking practical measures through therapy or counseling, then it is a valid reason for seeking divorce, for the Islamic principle states, “There shall be no inflicting or receiving of harm.” Zhulm (injustice) is not tolerated in Islam, regardless of who the perpetrator is.

2. Failure to fulfill the objectives and purposes for which marriage was initiated. This can be utter incompatibility between the partners, which may be expressed by their irreconcilable differences in temperaments, likes, and dislikes.

3. Marital infidelity. This can be a major cause for dissolution of marriage, for marriage is built on trust and confidence. Its main purpose is to preserve the chastity and modesty of those involved. Once this foundation is eroded and undermined and there is no chance to restore the same, then divorce is the way to go.

4. Failure of the husband to provide. When the man, who is considered the provider and maintainer of the family, fails to shoulder his responsibilities and the wife decides that she cannot continue tolerating his shirking of responsibility, this is grounds for divorce.
any one of the above-mentioned reasons can be considered as a valid ground for divorce in Islam. If in a legitimate case warranting a divorce a husband refuses to divorce his wife, then she is certainly justified by Islamic Law to approach the proper legal authorities to get a divorce: The judgment of divorce thus rendered by such authorities can be deemed as valid in Islam.

Excerpted, with slight modifications, from: www.islam.ca