Weasis is a multipurpose standalone and web-based DICOM viewer with a highly modular architecture. It is a very popular clinical viewer used in healthcare by hospitals, health networks, multicenter research trials, and patients. Weasis DICOM viewer is cross-platform, free/libre and open source software (FLOSS), multi-language and allows a flexible integration to PACS, RIS, HIS or PHR. This multi-platform DICOM viewer runs on Windows, Linux, and Mac OS X. It allows high-quality renderings with high performance through the OpenCV library.