The Blue World Institute, within the LIFE Delfi project, which is co-financed by the European Union through the LIFE program, has developed the Marine Ranger application for mobile devices. The application allows all interested citizens to become “citizen scientists” and join the activities of monitoring marine mammals – dolphins, whales and monk seals. The app allows you to share your sightings of marine mammals with scientists whenever you are at sea, fishing, diving, sailing, swimming or just enjoying the beach time. By collecting information from sightings of marine mammals, we can significantly improve their research and protection, as this makes it easier to identify areas of presence of individual species, trends in their abundance and especially the occurrence of rare and new species. The application is also intended for fishermen who can report by-catches of dolphins in nets and thus help determine which fishing tools have more significant interaction with dolphins. This supports research aimed at developing measures to reduce the interaction and damages that dolphins do to fishing gear, thereby reducing the economic loss to fishermen and dolphin mortality. The application allows you to report your sightings from previous years. Such sightings may be particularly important as they may supplement information on the presence and abundance of individual species in areas not covered by the surveys. Past observations can also help track the appearance of new species that are increasingly common in the Mediterranean and Adriatic due to environmental changes and global warming. Also, citizens often encounter injured, stranded or dead dolphins found on shore or in the sea. At that point, it’s not always easy to determine who to contact. By using the app and selecting the status of the animal found, the app will offer you the option to call the number of a service or organization that can arrange care and assistance. If you do not want to make a call, the application will automatically forward notifications about dead and injured animals to the competent services and organizations, which will organize assistance as soon as possible. To make it easier to find the animal and gather the necessary additional information, please leave your exact details in the app so that they can contact you as needed. Finally, if you are interested in marine mammals, through the app you can find out more about all the species that have appeared in the Adriatic and Mediterranean seas throughout history, and you can also have a look at what other marine rangers have reported. Invite your friends to join the app and participate together! You can download the application at www.marine-ranger.org. The application “Marine Ranger” was developed within the project “LIFE Delfi – Reducing the interaction with fisheries” which is co-financed by the European Union through the financial instrument LIFE.The views expressed in this publication are the sole responsibility of Life Delfi team and does not necessarily reflect the opinion of the EU.