The IEEE International Symposium on Biomedical Imaging (ISBI) is the premier forum for the presentation of technological advances in theoretical and applied biomedical imaging. ISBI 2021 will be the 18th meeting in this series. The previous meetings have played a leading role in facilitating interaction between researchers in computer science, medical, and biological imaging. The 2021 meeting will continue this tradition of fostering cross-fertilization among different imaging communities and contributing to an integrative approach to biomedical imaging across all scales of observation. We aim to keep a workshop at the conference on the topic of reliable multimodal/correlative processing and analysis, which are of primary interest for WG4. A number of invited and contributed presentations targeting the topics of WG4 and within the general scope of COMULIS will provide valuable input regarding state-of-the-art methods to be incorporated in the WG4 benchmarking efforts. The current status of WG4 activities such as software and algorithm repository, structured and automated evaluation, ontology, etc., will be shared. The workshop will also provide an excellent opportunity to attract new members to WG4 and COMULIS.