Salamu `alaykum, Rape generally falls beneath the category of zinaa.

My questions are these: Is there a such thing as marital rape in the shari`ah?

On another note, is a man permitted to FORCE his wife to have sexual intercourse with him? this is obviously when she is naashiz and unwilling to have coitus.

Jazaakum Allahu Khairan

In the name of Allah, all praise is for Allah, and may peace and blessing be upon the Messenger of Allah and his family. To proceed:

For a wife to abandon the bed of her husband without excuse is haram. It is one of the major sins and the angels curse her until the morning as we have been informed by the Prophet (may Allah bless him and grant him peace). She is considered nashiz (rebellious) under these circumstances. As for the issue of forcing a wife to have sex, if she refuses, this would not be called rape, even though it goes against natural instincts and destroys love and mercy, and there is a great sin upon the wife who refuses; and Allah Almighty is more exalted and more knowledgeable.