In the business world, many organizations store, organize and update their records of activities in large databases. As years pass, huge amount of data is gathered within the systems of the companies. As the system grows fast, some problems in the comprehension and analysis of the data collected occur. On the other hand, companies should analyze the accumulated data accurately and get information from them in order to carry out some crucial functions critical to the survival of the company such as planning, forecasting and managing. The difficulties mentioned above have compelled the technology experts to find new solutions to assist the people taking part in the decision process and lacking in technical knowledge. In the recent years, the concept of data warehouse has begun to appear as a new type of complex decision support systems. A data warehouse can simply be defined as a pool of data that supports users in making strategic decisions. These data are organized in a way that will present easy use and excellent reporting performance. The subject of this study is to design and develop a data warehouse using the necessities and sales database of a retailer company. Firstly, data warehouse and the steps of data warehouse processes are defined, and then applied part is explained. The data warehouse application constituting the subject of this thesis is carried out in a middle-scale company that is in the food sector and has a nation-wide distribution net. This company has approximately 600 employees. In this study, a data warehouse has been designed in order to support the Sales and Human Resources Departments by using the data collected by Sales Field Organization of the company. The main objective of creating a data warehouse is to enable a better control of the Sales Representatives working in the Sales Field Organization by Sales Managers and provide the gathering of consistent and accurate data that will be used by Human Resources Department while preparing a performance measurement system. These data will also be used by the Sales Department while determining a sales policy for the company. In this study, powerful and easy-to-use MS SQL Server 2000 that includes data transformation and analysis tools is used.