This Bachelor’s thesis examines the founding of a small and medium-sized business and the building of an Open Source based electronic marketplace. In the beginning there is consideration about the company form and other fundamental questions about running the business. In addition, there are some questions regarding the electronic marketplace. There are no straight answers to these questions, but the solution for the electronic marketplace has been built of various components, which best serve the entrepreneur. The goals of this thesis were to get basic information on how to start a business, how to operate as an entrepreneur and how to build an Open source-based electronic marketplace for the business. The requirements for the electronic market-place where the following: easy controlling, a possibility to customize and a cost-effective maintenance. In this thesis the electronic marketplace for fishing gear is set up only on a virtual server as a local host. The reason why the electronic marketplace is not put up to the Internet is that the electronic marketplace is still only a plan and some of the elements need the Internet to work. However, the electronic marketplace has been built as close to the final version as possible, so that it could be released online later on. There is a model of the electronic marketplace as a attachment. The electronic marketplace requires Apache-, MySQL- and PHP– softwares to work.