This PhD project starts from the attested competition between the two main denominal verb-forming processes, i.e., affixation (which is the concatenating operation of adding a prefix or suffix to an input, e.g., a myth > to demyth, a nanny > to nannify) and conversion (which is a change a part-of-speech with no formal change, e.g., a myth > to myth, a nanny > to nanny). An ecological approach, borrowing concepts from evolutionary biology, is applied to the field of morphological word-formation. Competition, as described and studied in biological and social systems, refers to Darwin's “struggle for survival” and the notion that the “fittest wins” already drew a parallel between competition of synonymous forms and the Darwinian struggle for life. Gause's competitive exclusion principle, which states that two species with similar ecological niches cannot coexist in a stable equilibrium, has been applied to morphological competition. Two species (here, linguistic forms) competing for the same resources (i.e., meaning and distribution) cannot coexist; in such a case, either the less efficient form (i.e., the form that shows less productivity) becomes extinct or both forms coexist (i.e., remain somewhat productive) within distinct ecological niches. Before a resolution occurs, competing forms may coexist in temporary equilibrium, in which no competitor shows a clear advantage over the other. These “states of equilibrium” are expected from an ecological viewpoint and may persist over some periods of time. In synchrony, we can observe the transitory stages before resolution. The purpose of this research is to provide an overview of the formation of denominal verbs in present-day English, on the one hand, by studying converted and affixed verbs, and, on the other hand, by focusing on pairs of “formal doublets”, i.e., one converted and one affixed verb both formed on the same nominal input (e.g., to acronym / to acronymize, both formed on the noun an acronym). The dataset comes from two complementary sources: 355 converted verbs and 62 affixed verbs attested in the Oxford English Dictionary (OED) since 1950 and 171 suffixed verbs (all hapax legomena) from the Corpus Of Contemporary American English (COCA) attested since 1990. Among these 588 verbs constituting our dataset, 104 verbs are part of a “formal doublet”, such as, the converted verb to aerosol (attested since 1964 in the OED) and the affixed verb to aerosolize (attested since 1944 in the OED); the affixed verb to computerize (attested in 1960 according to the OED) and the converted verb to computer (attested in the COCA). The morphological, etymological, phonological, and prosodic analyses of the input nouns, combined with the semantic analysis of the verbal outputs, highlight the different factors and constraints which favour or prevent either verb-formation process. Moreover, the study of the formal doublets reveals which criteria have no, or very little, impact on the competition between conversion and affixation. Our analyses show a complementary distribution where each verb-forming process seems to have found its specific niche. For example, the morphological analysis shows that regular nominal compounds resist affixation (99% of the compounds in the dataset are converted into verbs); the phonological analysis shows that inputs of four or more syllables tend to favour suffixation (about 68% of the inputs of four or more syllables are formed by affixation and there are no attested formal doublets formed on these inputs); the semantic analysis of the verbs reveals that affixation is markedly preferred to express a resultative meaning, whereas conversion is favoured to form performative or instrumental verbs. Finally, the analysis of the 104 formal doublets enables us to study semantic competition in synchrony: almost half of the formal doublets are constituted of two verbs expressing different meanings, hence not in semantic competition.