This document is an editorial for a special issue of the journal Biomedicines on the topic of theranostic drug delivery. Theranostic refers to a methodology that combines disease diagnosis and treatment. It is considered a promising technique in precision medicine, particularly for cancer detection and treatment. The editorial highlights the use of carrier systems to target tumor cells and minimize adverse effects. The special issue includes research articles from authors in 14 different countries, covering various applications of theranostic techniques. The editorial concludes by expressing hope that the articles will inspire future research in this field.