This study analyses the legal framework governing investments in the mineral and petroleum sectors in Tanzania. It investigates the mining and petroleum legal regime’s impact on ensuring that the country and its citizens obtain maximum benefits from mineral and petroleum investments. The study employed qualitative method; it has combined both library and Internet research as well as interview. The study intended to ascertain potential significant impact of the legal framework governing mining and petroleum investments on ensuring maximum benefits for the country and its citizens. This study discovers that at different periods, the legal framework governing investment in Tanzania, particularly investments in the mineral and petroleum sectors, has been founded with principles of law which do not carry in them the best interests of the country to guarantee maximum benefits for the country and its citizens. These principles have affected the aspects of investment law owing potential significance to ensuring maximum benefits for the country and its citizens, namely; fiscal framework; local content; employment, training and transfer of technology; compensation for relocation and resettlement for local population whose land rights have been violated in the course of investment operations; free carried interest; corporate social responsibility (CSR); and empowerment. This study recommends for the government to incorporate in its investment law, particularly laws which govern mineral and petroleum operations, principles and theories which provide for the right of natural resource rich states and their people to benefit maximally from their use of resources as a remedial measure. Such are the principle of Permanent Sovereignty over Natural Resources (PSNR) and the theory of resource nationalism.