Taxation remains a veritable instrument for national development. Apart from being a major source of revenue for the government, taxation provides goods and services needed by citizens. Taxation policies can stimulate economic growth and job creation through its impact on investment and capital formulation in the economy. In this respect reforms in the tax system that ensure effectiveness, equity and efficiency are conditions for healthy public revenue. The decision to reform the Nigerian tax system is crucial in order to improve the revenue base for national development and attaining socio-economic goals for taxation. The thesis which adopts the doctrinal approach examines the process that led to the current tax reforms under the Federal Inland Revenue Service (Establishment) Act, 2007 and the reforms initiated by the Act; the impact of the tax reforms under the Act on tax administration at the federal level; and the gap and challenges faced in the implementation of the reforms. The findings of the research are that the reforms in the FIRS have resulted in a review of tax laws, reduced the delay in policy initiations and implementation, creation of a customer friendly tax environment, improvement in staff training and welfare, greater accessibility, review of procedures and processes as well as utilization of information communication technologies. These have positioned the FIRS as a modern and efficient tax administrative agency and have redefined the role of taxation as an important means of generating revenue from non oil revenue sources. The research examines some of the challenges which include persisting cases of corrupt tax officials, centralization of tax administrative agency and the conflicts between the FIRS (Establishment) Act, 2007 and Company Income Tax Act 2011. The self assessment regime which in the past did not function properly, has under the last reforms gained ascendance as the major mode of tax assessment and the uncertainty that hitherto characterized the process has been resolved to a large extent by the FIRS (Self Assessment) Regulation 2011, by setting out processes, procedure and providing standard guidelines for the implementation of the established Self Assessment Regime in support of an efficient tax administration system in Nigeria