On behalf of the organizing committee, it is our great pleasure to invite you to the 4th International Conference of Materials, organized by MDPI’s Open Access journal Materials. This conference will be held in the beautiful city of Barcelona The first three editions of the conference were in electronic format, and each was a great success. This has encouraged the organizing committee to take this tradition to the next level by organizing the 4th edition of this conference in Barcelona, where all stakeholders working on various aspects of materials science and material engineering can come together. The aim is to make this event a forum for discussion, knowledge exchange and fruitful interactions among participants in this exponentially growing field.