The first part of the technical design project introduces the SXP project in the framework of the European XFEL and the baseline instruments. The introduction chapter revises the properties of SASE3 FEL radiation and proposed extensions to improve its performance. The remaining chapters describe the scientific applications proposed so far by the scientific community: The contribution of the Time-Resolved X-Ray Photoelectron Spectroscopy (TR-XPES) consortium is described in Chapter 2. The proposal to use soft X-ray spectroscopy of high-valent metal intermediates in biological and inorganic catalysts for chemical bond activation is summarized in Chapter 3. The possibility of using SXP as a laboratory for astrophysics, atomic physics, and fundamental research with highly charged ions is outlined in Chapter 4. Finally, the use of SXP to develop new diagnostics or experimental techniques is presented in Chapter 5. These science cases, techniques, and experimental setups will extend the portfolio of European XFEL beyond the baseline.