This book explores the relationships between the age of an enterprise, the resources held by an enterprise and the effectiveness of the enterprise's systems of internal controls in small businesses in Nairobi, Kenya. Further, this book explored the relationship between the effectiveness of internal controls and financial performance of an enterprise. The study establishes that there were deficiencies in the systems of internal controls. However, the degree of deficiencies varied from one enterprise to another. The components of internal controls that were weakly instituted were risk analysis and lack of proper flow of information. The author established that there is a negative relationship between the age of an enterprise and effectiveness of its system of internal controls. In addition, the findings establish that there is a strong negative correlation between resources held by an enterprise and internal control weaknesses. The author also establishes that there is a weak negative relationship between internal controls weaknesses and financial performance of an enterprise.