NIDIO is an open-source code infrastructure assisting with the use of Dutch administrative register data. It is built around administrative data provided by Statistics Netherlands (CBS) in the Microdata Services Remote Access Environment (RA). NIDIO facilitates the study of inequality within and between Dutch organizations by integrating various administrative source data into a harmonized three-level data structure (organizations, individuals, and jobs). NIDIO helps to reconstruct workers’ demographic profiles and employment outcomes (e.g., wages) and links them to organizational characteristics. NIDIO achieves these aims by addressing three challenges that are commonly encountered while working with linked employer-employee register data: 1. Preparing and linking administrative data sources involves several decision-making steps that often remain undisclosed in published research. NIDIO provides transparent data processing routines that improve the reproducibility of completed analyses. 2. Users with limited prior experience working with linked employer-employee register data face high startup barriers during project setup. NIDIO eases time- and labor-intensive data processing by providing tailor-made and customizable installation tools. 3. Translating administrative data into social science concepts and measures is a nontrivial task. NIDIO provides guidelines and best practices to bridge the gap between administrative and scientific data. NIDIO is managed by Christoph Janietz (c.janietz@rug.nl) and Zoltán Lippényi (z.lippenyi@rug.nl) at the University of Groningen. The NIDIO code was developed by Christoph Janietz and Zoltán Lippényi as part of the NWO-funded project "Beyond Boardrooms". GitHub: github.com/christophjanietz/NIDIO-Code OSF: osf.io/9b2xh