Micro and Small Enterprises (MSEs) create jobs and contribute to innovation and economic development. The MSE Act, 2012 provides a legal, institutional and regulatory framework for the promotion and development of MSEs in Kenya. The five major objectives of the Act are to provide an enabling business environment, facilitate access to business development services for MSEs, facilitate formalization and upgrading of informal MSEs, promote an entrepreneurial culture and promote representative associations. The Act provides for the creation of the MSE Authority which is responsible for implementing the Act. The purpose of this study was to examine the effectiveness of this Authority in implementing the MSE Act 2012. The research objectives were to determine the extent to which the MSE Authority had implemented the Act, to examine the challenges the Authority had faced and how they had moderated its expected outputs and to discuss how the Authority had mitigated these challenges. Using top-down and bottom up theories of policy implementation as a theoretical framework, the thesis of this study was that success or failure of the MSE Act 2012 depended on how it is implemented. The study applied a qualitative case study design. Using purposive sampling to identify senior officials of the MSE Authority, the researcher identified respondents who could speak to the intentions, plans and performance of the Authority. The data was analysed using framework analysis based on the research questions and the objectives of the Act. The study found that the MSE Authority had only partially implemented the MSE Act 2012. The challenges that the Authority faced that moderated its output were the failure to operationalise key provisions of the Act including establishing the Office of the Registrar of MSE Associations and the MSE Fund. The Authority also suffered from chronic underfunding and understaffing. There were other government agencies with similar mandates which resulted in duplication of efforts, wastage of resources and interagency conflict. Recommendations of this study are that objectives of the Act should be clear and consistent, the link between the Act and the intended outcomes should be clear, the provisions of the Act should be fully operationalized, and a timeframe should be established for this, with incentives and sanctions for all agencies and stakeholders involved in the implementation of the Act. The Authority’s capacity should be improved by recruiting full time qualified, committed staff with relevant experience. For all of these to happen, support from political leadership is critical