What are the differences between lookup relationship and master-detail relationship?

Answer: In master-detail relationship if parent record is deleted, then all the associated child records get deleted. In lookup relationship if parent record is deleted, then all the associated child records are not deleted. In master-detail relationship each child record must compulsorily have a parent record. In lookup relationship child records can exist without having parent record. Roll-up summary field is available for master-detail relationship only.