The world of media is strongly impacted by the digital revolution: means of production, publishing, and broadcasting broaden and users' practices evolve, changing on the way established economic rules. The CrossMedia Observatory aims at building processes, tools and methods to analyze and better understand the challenges and the evolution of the media sphere. Our objective is to create an integrated system allowing the analysis of a large range of information sources, web sites (blogs, Press, TV and Radio websites), newspapers, Radio and TV media streams in a large period of time (12 to 18 months). More precisely, we want to detect, identify, monitor, measure, analyze, and study the spread of media events and their derivatives. The CrossMedia Observatory project is driven by the needs of social sciences research and of information protagonists. This strong collaboration between scientific research and social science aims at developing new concepts and analytical tools able to characterize the evolution of the media sphere. The project gathers partners from several research domains: linguistic and text analysis, transcription, computer vision, search engines, and visualisation. Each scientific partner brings not only their expertise in their field, but also makes available to the project high performance software. Therefore the project may focus on the main technological bottlenecks and challenges: formalisation of the crossmedia objects with relations and event concepts; transcription enrichment from cross media resources; discovery and tracking of events and dynamic visualisation. Additionally those are processed on very large scale data. The strengths of this project lie in the synergy between IT and social science research, the development of high performances tools, together with resource diversity and volume. The ambition of the TransMedia Observatory is to make the relationship between the Internet, press, radio and television broadcasts more intelligible, viewable and searchable at a macro-level of analysis, The automatic tracking and monitoring of media entities and events at a variable temporal granularity will facilitate this. If the proliferation of media sources that broaden users' practices is a reality, does it ensure nevertheless the information plurality? Who produced the information? Who is the source? These questions are a matter of general interest for the society of today and tomorow.