This document describes the project plan for ESCAPE Work Package 5, ESAP - ESFRI Science Analysis Platform, detailing its goals, objectives and structure. It will serve as the work plan at the beginning of the project and will be updated throughout the project. The ESAP main objectives are to define and implement a flexible science platform for the analysis of open access data available through the EOSC environment that will allow EOSC researchers to identify and stage existing data collections for analysis, tap into a wide-range of software tools and packages developed by the ESFRIs, bring their own custom workflows to the platform, and take advantage of the underlying HPC and HTC computing infrastructure to execute those workflows.