The efficient and effective use of data is the backbone of any MRV system or application. Both in reliability and quality of the outcome, as in the efficiency and costs associated with reaching this outcome. In this deliverable we explore the relevance and need for adequate data for MRV, introduce the MARVIC metadata catalogue that aims to facilitate easier and more effective search for and discovery of datasets for MRV and elaborate how the 4R principle (Right source, Right rate, Right time, Right place) often used in for example fertiliser management can be applied in the context of selecting data for MRV for soil organic carbon in an efficient and effective way. The deliverable is relevant for anyone involved in or interested in finding, selecting or providing data for MRV applications or other spatial projects, from the local to the European scale. These include MRV operators, land managers, advisors, researchers and governmental organisations. A metadata catalogue facilitates the easier discovery of data, knowledge and information resources by collating metadata from a variety of sources in a single location with added search functionality. In the MARVIC project, we have deployed an open metadata catalogue using existing open-source software, current metadata standards, and have customised this catalogue specifically for MRV applications. To this purpose we have translated the 4R principle used in fertiliser management to data for MRV applications by creating the 4 categories of Right Data source, Right MRV use, Right quality and Right Resolution. For each category the meaning in the context of MRV applications is elaborated and its application in the metadata catalogue is described. For some of the R’s this is reasonably straightforward and the application can be facilitated by customised filters on keywords in the metadata. For others, the general application principles are described but further facilitation by semi-automation is difficult, since the data requirements following the application of the 4R principles are quite MRV project dependent and the quality and content of the metadata does not always allow automation. A general conclusion of this work is that a domain specific metadata catalogue and domain specific elaboration of data selection principles can be beneficial to the domain community. However, a limiting factor at present is the quality and completeness of metadata annotation. Thus, continued attention, awareness raising, and capacity building on the topic, for example in the context of the Mission Soil, the Carbon Removals and Carbon Farming (CRCF) Regulation and the wider MRV community is important. This includes the development of domain specific terminology and the transposition of this terminology to machine readable vocabularies to facilitate metadata and data annotation to such an extent as needed for efficient and effective MRV applications.