The most important resource in all projects is people. Project success depends on choosing the right people for the job, and then making sure that they are kept informed, well motivated and provided with all the tools and other resources that will enable them to complete their tasks. This chapter examines not only how different project organization structures can influence people and affect communications between them, but also how the organization can either damage or enhance the management task. Organization theory in businesses has occupied the minds of behavioural scientists for over a century, but formal organization structures can be traced back to the beginnings of history, particularly in churches and armies. The subject is complex. Choosing the organization structure that best suits a particular business of project is not always cut and dried, and in some circumstances competing companies might fare equally well even though their organizational structures differ considerably.