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. A flexible integration to any PACS, RIS, HIS or PHR can be done with the DICOM and DICOMWeb standard interface. It allows high-quality renderings with high performance through the OpenCV library. It has been designed to meet several expectations of clinical information systems and their future evolution regarding medical imaging: providing web-based access to radiological images, as well as covering a considerable number of DICOM types and offering multimedia capabilities.