The P-GRADE Grid Portal is a web based, service rich environment for the development, execution and monitoring of workflows and workflow based parameter studies on various grid platforms. P-GRADE Portal hides low-level grid access mechanisms by high-level graphical interfaces, making even non grid expert users capable of defining and executing distributed applications on multi-institutional computing infrastructures. Workflows and workflow based parameter studies defined in the P-GRADE Portal are portable between grid platforms without learning new systems or re-engineering program code. Technology neutral interfaces and concepts of the P-GRADE Portal help users cope with the large variety of grid solutions. More than that, any P-GRADE Portal installation can access multiple grids simultaneously, which enables the easy distribution of complex applications on several platforms.