This theme uses a panoply of approaches from different disciplines to investigate both the internal and external factors that play a role in the emergence of linguistic diversity. One approach to investigating language-internal change is descriptive, reconstructing the sequence of changes that take place during the history of a language family; another is explanatory, elucidating the potential causes of internal changes in the cumulative amplification of minute biases - of a cultural or biological nature - over centuries. As for the external causes of diversification, these can be linked to the environment, both social (leading to language contact and also to competition between languages) and physical. A third aspect of the research conducted in this theme reaches deeper back in time by studying communication among our closest relatives , the bonobos, with the potential of shedding light on the evolution of human language.

The Language description theme aims at the description of under-described and undocumented languages, which are often endangered, at different levels of their system: phonology, morphosyntax, semantics, and discourse. The descriptions that we produce are situated in a twofold perspective, both typological and areal, and they are based on fieldwork that we carry out within communities in their cultural and ecological environment. In our approach to language description, we pay particular attention to our , the validity of our data collection methods, and sharing our data and results with the communities. Our approach consists of combining various methods, including both the collection of spontaneous speech samples and elicitation using direct elicitation techniques (based on translation) and indirect techniques (based on visual stimuli). Beyond the study of under-described languages, our research also concerns well-known languages, with the aim of investigating some lesser-known linguistic facts of these languages or re-examining them in the light of the typological approach.

The Typology theme studies the diversity of the ways that different linguistic categories are expressed across the languages of the world, and it includes work in morphosyntactic and semantic typology. The originality of our research in typology lies in the fact that it is based on descriptions of under-described and undocumented languages and on first-hand linguistic data. Our approach to typology is inclusive in that we seek to identify typologically interesting phenomena in the languages we study and to contribute new data to existing typologies, thereby making them evolve. Moreover, it is areal in that it takes into account contact between languages, whether these are genealogically close or distant.

The theme Endangered Languages: Fieldwork – Description/Documentation – Revitalization (LED TDR) , which started in 2009, unites those members of DDL who work on the description and documentation of endangered languages (EL) in different parts of the world. LED TDR coordinates the Language Revitalization Network (LRN), an international network with the University of Oregon Department of Linguistics as its principal partner.
Its objective is to contribute to the intellectualization of the issues surrounding work on EL by using a contrastive approach for parallel analyses of a great variety of EL situations, in particular of highly endangered languages.
Its major topics of research are the specificities of fieldwork on EL (for either description, documentation, revitalization), the analysis of the great diversity of the sociolinguistic contexts of EL, and the linguistic and social challenges of their revitalization.
The team offers support for students and junior researchers working on the description and documentation of EL, with a particular attention to the ethical aspects of such work in such very sensitive field situations.