The district court did not abuse its discretion in certifying two California and one national classes in a suit by detained immigrants against the private company that ran the detention centers. The defendant’s written corporate policies required inmates to work, cleaning bathrooms and other public areas under threat of discipline, and the defendant had a policy of misclassifying inmates as having signed up for its voluntary work program when they had not. Those common issues predominated over individual issues, such as damages. At the class certification stage, it was not necessary to narrow the class definitions to encompass only persons with claims within the statute of limitations, nor was it necessary for the plaintiffs to present a complete damage model at that stage.