**Preface to "Heterocyclic Compounds from Marine Organisms"**

Marine natural products have played an important role in the development of new bioactive compounds with a variety of interesting properties (antiviral, cytotoxic, antitumor, anti-inflammatory, antimicrobial, etc.). Within the molecules these marine organisms produce, the presence of heterocyclic subunits is quite frequent. The structural diversity of this group of marine compounds, together with their diverse biological activities, have attracted the attention of the scientific community. This Special Issue on "Heterocyclic Compounds from Marine Organisms" aimed to provide an overview of the most recent developments related to the isolation, characterization, synthesis or biosynthesis of marine compounds containing heterocyclic units or their analogs. The authors who contributed to this Special Issue are gratefully acknowledged. We hope that readers will be interested in this content.

> **Asunci ´on Barbero** *Editor*
