The objective of this thesis is to investigate how the influences of the Internet on the Organisational Buying Behaviour of professional services can be characterised. The way organisations purchase services is one of the most important questions to the business marketing managers of today. The buying of professional services by organisations is complex and difficult to analyse. Each organisation has their own way of purchasing and these ways are better known as the organisational buying process. The people involved in this process form the buying centre, and the factors that influence the buying organisation are the influencing factors in the Organisational Buying Behaviour. In recent years access to new techniques is easier and cheaper. More and more companies adapt their system to the Internet. The Internet offer different blends of opportunities to companies due to variances in speed of, control over, and access to communication and distribution channels. The Internet as a marketing channel will revolutionise the service business. However, this depends on how many added values there are in the Internet communication. These communications and distribution functions will change the traditional way of conducting business. The Organisational Buying Behaviour is a complex and dynamic process that requires plenty of information. Purchasing professional services involves a lot of risks, time and money. Selection of professional services requires information, knowledge and know-how about the related subject and area. However, Internet provides the seller and the buying company, opportunities and access to information and eases the way to find what is required. At the same time this communication tool is threatening to change and influence the way businesses are conducted. Therefore, marketers have to identify the reasons to, and have an understanding of, how the influence of Internet can affect different processes. The investigation in this thesis was conducted through four case studies. The necessary data collection was performed through four personal interviews. The survey of literature contains different models within the frame of Organisational Buying Behaviour of professional services, such as, the buying process, the buying centre and the influencing factors on the Organisational Buying Behaviour. Also, theories regarding the Internet and different communication models are described. These models are discussed further in the frame of references. The result of the case studies shows that the influences of the Internet affect the buying process in a way that makes the process faster and more efficient. However, the buying centre was not considered to be affected. The respondents did neither believe that the influences of Internet had changed the influencing factors in the Organisational Buying Behaviour. These results are based on the information that was available at the time when the data was collected. Additionally I had the possibility of interviewing only one person at each selected company.