The subject of this thesis is a web application for the IQSYS Information Technology and Consulting Private Company Ltd. It is aimed to store the company’s most important clients, their information and the company’s plans with them. The offline, Excel and PowerPoint-based system, that was used so far, is to be replaced with this new, online application. It is developed with Microsoft Visual Studio 2010 and .NET 4.0 framework. The company’s database was used with Microsoft SQL Server 2008. The application was developed with Silverlight technology, making it easy to reach online and for the modernized development. I was instructed to make the User Interface look like the old system. The application stores the client’s current state, the future common options, the industrial review, the SWOT analysis and other connecting information. It stores the connection web, the client’s structure, and the company’s group that is in connection with the client, the group’s future plans and the company’s SWOT analysis. All stored data is editable. The company’s competitors can be linked to a client with all the needed information stored. The services that are given from our company to the client can be viewed, and IQSYS’s planned activities can be managed and linked with resources. The application stores every data archived, nothing is deleted physically, so later the old information can be extracted. The current user can set which clients to be shown, and they can filter the clients by type. The application contains an administration interface, where the administrators can check event and error logs, set rights and roles to new or old users, and manage the competitors and companies. The application can get data about users from the PMTOOL program (that is the project controlling tool of IQSYS). The application is finished according to the specification in the given time, and new ideas came up, that will be implemented later.