This doctoral dissertation analyses the ecology of linguistic diversity of Zadar. The ecology of language diversity involves the description of the interrelationship between languages, speakers and the community in which those speakers use languages. Two research methods have been used for the description of the ecology: the first one is the analysis of the linguistic landscape of Zadar, which was used to investigate the use of written language in the public space; the second one is a qualitative method and involves semi-structured interviews with passers-by, owners and managers of shops, and with decision makers on the local-government level. Considering the fact that Zadar is located at a strategically very interesting part of the Eastern Adriatic coast, historically it has always been interesting to numerous conquerors. Due to that, the town has been accepting population from various parts of Croatia and Europe and traces of languages and dialects of those people are still present in the linguistic ecology of Zadar. The linguistic landscape of Zadar still shows traces of historical linguistic diversity, especially on infrastructural objects from the Austro-Hungarian and Italian periods and on the municipal cemetery. However, most examples of historical linguistic diversity in the public space have been erased in the course of social changes. The research findings show that the main language of communication in Zadar is Croatian, based on the linguistic landscape and on the interviews. Croatian is the most frequent language in the public space and the only one on official signage. Besides Croatian, other languages are used in business and tourism, but English is the most frequent foreign language in the linguistic landscape. English has become a universal foreign language used for communication with all foreign tourists and has slowly pushed out other foreign languages in tourism. English is equally important to passers-by and employers, who consider it a prerequisite for employment, so that their employees may effectively communicate with the clients. The research findings obtained by interviewing accord with the findings obtained from the linguistic landscape analysis and point to tourism as the main force that influences almost all aspects of written and spoken language use in Zadar. The results also show the seasonality of the linguistic landscape of Zadar, in which the out-of-season advertising shows mainly Croatian, while in-season advertising shows the use of Croatian and English, or only English. The linguistic landscape of Zadar is dynamic and it changes in accordance with trends and needs of the inhabitants. Different languages in the linguistic ecology of Zadar belong to diverse ecolinguistic niches in which their practical and communicative value is diverse.