This special issue, dedicated to myocardial classification, is meant to illustrate the current state of cardiac imaging for characterizing myocardial tissue phenotypes in various cardiac diseases. All of the articles in this issue are related to magnetic resonance imaging, not because there was a mandate to focus on one imaging modality, but rather because as imaging modality MRI offers excellent capabilities for myocardial tissue characterization and classification, and has in fact established itself as a modality of choice. In this context, the T1 and T2 relaxation properties, and the introduction of techniques to map these properties in the myocardium have over the last few years received most attention, and by no means has the potential of these approaches been exhausted yet for the purpose of diagnosing disease, aiding in differential diagnosis, and establishing new biomarkers that can be used to evaluate therapeutic interventions. A substantial fraction of the articles in this issue therefore relate in one form or another to T1 and T2 mapping in ischemic and non-ischemic heart diseases. This special issue also includes less common applications of myocardial classification such as it’s use for interventional procedure guidance. The field of myocardial classification has developed enough breadth that a special issue with invited reviews and original research contributions can only provide a partial view. The choice of contributions in this issue is therefore not meant to be comprehensive but instead illustrate the diversity of the field, and take stock of the progress achieved so far, and also point the various open questions and knowledge gaps that remain. The choice of topics and contributions from leaders in the field owes much to the great efforts of the co-guest editors, Dr.’s Fereira, and Piechnik (University of Oxford), and Dr. Bax (Leiden University Medical Center). And most importantly, we take this opportunity to thank the authors of the contributions to the special issue for generously sharing their experience and insights!