The development of a specific materials database and handbook, for engineering design of in-vessel components of EU-DEMO, is an essential requirement for assessing the structural integrity by design. For key in-vessel materials, including EURFOER97, CuCrZr, Tungsten and dielectric and optical materials, this development has been ongoing now within the Engineering Data and Design Integration sub-project of the EUROfusion Materials Work Package for several years. However, the status still is that presently none of the mentioned materials exist in established nuclear codes and currently have in-sufficient data to ensure reliable engineering design and safety. In this paper an overview of the current status of EU-DEMO database and handbook for these key in-vessel materials is provided. This comprises highlighting the practical steps taken to obtain the raw data, screening procedures and data storage, to ensure quality and provenance. We also discuss how this procedure has been utilized to produce materials handbook chapter on EUROFER97 as well as the critical challenges in data accumulation for CuCrZr and Tungsten, planned mitigations and the implications this has on structure design. Finally, key principles and philosophy behind our strategy to develop the materials database and handbook for the in-vessel materials are outlined, including concepts to accommodate sparse irradiated materials data, links to design criteria and importance to EU-DEMO engineering design.