The research reported in this dissertation investigates extending the power and flexibility of an object-oriented language with inheritance, Static typing, and concurrency. A language supporting inheritance, static typing, and concurrency offers a significant leverage in software development. However, when these features are provided together, the benefits of the features are significantly reduced due to the interaction among them. The challenge for the designer of an object-oriented language lies in the difficulty of reconciling the conflicts among these features. This thesis discusses two issues: combining static typing with inheritance and combining concurrency with inheritance. A new model of type and inheritance, called HANA, is presented. The HANA model integrates multiple inheritance, multiple representation, method exclusion, and method name overloading with static typing. The contribution of HANA is that it extends other existing models of type and inheritance with enhanced expressive power, increased reusability, and improved program efficiency. Combining concurrency with inheritance is investigated in the framework of the actor computation model. A language design based on the actor model of concurrent computation faces a serious problem arising from the interference between concurrency and inheritance. A similar problem also occurs in other concurrent object-oriented languages. The problem of concurrency-inheritance conflict is described and a solution based on a concept called behavior abstraction is presented. / Ph. D.