Weasis is an open-source DICOM viewer available for free, designed for both standalone applications and web-based environments, characterized by its highly modular design. It finds extensive application in various healthcare contexts, such as hospitals, health networks, multicenter research studies, and even for personal use by patients. As a cross-platform solution, Weasis seamlessly integrates with systems like PACS, RIS, HIS, or EHR, providing versatility in its usage. The viewer utilizes the OpenCV library to ensure high-performance rendering and exceptional quality in medical imaging. Starting from version 4, Weasis boasts a user-friendly interface that adapts to different operating systems, optimizing the viewing experience on high-resolution displays. Among its notable features is compatibility with a diverse array of DICOM file formats, including multi-frame, enhanced, MPEG-2, MPEG-4, and others. Additionally, users can easily import DICOM files using DICOM Query/Retrieve (C-GET, C-MOVE, WADO-URI) and DICOMWeb (QUERY and RETRIEVE) protocols, as well as manage DICOM data on CDs or DVDs with DICOMDIR. Furthermore, Weasis continues to evolve, incorporating user feedback to enhance functionality and performance over time.