The archive of Castle De Haar consists of written records, over 6,000 drawings, photographs, slides and (glass) negatives, fabric and wallpaper samples and stencils. The archive also contains records of the building process, including daily and weekly reports, copy books of correspondence, specifications and extensive financial records. It contains study, situation, design, and working drawings that provide insight into the design process of the castle, the châtelet (gatehouse), the church, the village of Haarzuilens, the parks and gardens, and even the furnishings and decoration of the hundreds of rooms. Thus the designs of the stained-glass windows are present, as well as the marble, wooden and tile floors, the furniture, wallpaper, crockery and even the costumes of the servants.