Computational grids have become an important tool for various scientific disciplines to contact research, providing access to vast amount of disperse computing resources. This trend is particularly exemplified by the world-wide collaborations and international projects that develop software tools and deploy large scale grid infrastructures to enable eScience. Open source software plays an fundamental role in this context. Thanks to open source initiatives, scientists have access to high-quality software implementing functionality spanning all aspects of computing. Starting form the grid-middleware itself, to general purpose high-level tools (program solving environments, portals, workflow engines, etc) and finally to discipline specific software enabling research in various scientific domains (High Energy Physics, Computational Chemistry, Biomedicine, Meteorology etc). This talk will provide an overview of the state of the art of science contacted within grid computing environments and will highlight the important role of open source software.