Semantic technologies have reached a mature stage: the result of years of research is a set of tools and techniques for creating and processing semantics. However, the participation of users in tasks around semantic content creation is still limited. This thesis investigates existing processes of authoring semantic content to show the role and necessity of human engagement in these processes. The contribution of the thesis are best practices, guidelines and suggested tool support for incentives-driven semantic content creation. It will include participatory design and integrated organization and technology development methods to encourage users to create semantic annotations for various content: text, images, audio and video data, and Web services.