Abstract Einar Haugen is generally regarded as the founding father of ‘language ecology’ or ‘ecology of language’. In his classic 1971 paper, he suggested that “[l]anguage ecology may be defined as the study of interactions between any given language and its environment”. After tracing the roots of language ecology in the social sciences and biology and the use of similar locutions by other linguists before him, the present paper discusses major conceptual and theoretical issues surrounding his proposal. Fundamental discrepancies between how the concept of ecology is understood in biology and sociology, on the one hand, and the attempted application to language, on the other, render details of Haugen's framework disputed. In particular, it is difficult to transpose the three central bio-ecological concepts of organism, environment, and relationship/interaction to human language, and in his ecological-linguistic work, Haugen wavers between placing the focus on the interaction, on the interrelation, and on the ‘organism’, i.e. in his case language. He primarily treats language ecology as a metaphor, but occasionally speaks of language ecology as a scientific field. Moreover, as its object of study is not sharply delimited, its relations to other research objectives or neighboring disciplines are unclear. Furthermore, the grand scope of his program often entails severe difficulties in actual research that is limited in time and by available resources. In principle, however, the holistic, multi-faceted and dynamic perspective of his approach constitutes a valuable corrective to linguistic approaches concentrating one-sidedly on language as an autonomous, static, synchronically quasi-invariable system. This fact provides a major reason for the notable impact of his 1971 article on subsequent sociologically and ecologically oriented linguistic research.