Since its first detection in Southern China in 1996, highly pathogenic avian influenza virus (HPAIV) H5N1 has emerged as a major global health threat and spread across three continents. In Africa, Mali was considered a country at high risk and surveillance of HPAIV H5N1 was complicated by the endemicity of another highly lethal poultry virus producing similar symptoms, Newcastle disease virus (NDV). The general aim of this thesis was to improve our understanding of the epidemiology of avian influenza (AI) and Newcastle disease (ND) in Mali and produce recommendations for improving the surveillance and control of these diseases. Prevalence/incidence studies showed: a low circulation of AI viruses (AIVs) -although higher in villages located in the inner delta of the Niger River where large populations of wild water birds migrate- and seemingly no particular epidemiological role of domestic ducks; a high circulation of NDV influenced by seasonal, geographic and flock (number of Guinea fowl, access to a pond) factors. Poultry production and trade studies revealed: a largely informal commercial poultry sector, mainly peri-urban and of low biosecurity level; characteristics of village poultry farming more (free-roaming, inadequate quarantine and sick/dead bird disposal) or less (high ND vaccination coverage, low palmipeds' density) favourable for AIVs and NDV transmission; mainly rudimentary low-biosecurity live poultry markets and a hierarchical structure of poultry trade network to/from the Sikasso district with four hubs identified based on network centrality measures. Evaluation of HPAI and ND surveillance found: a well-organised surveillance network but functioning only moderately satisfactorily, lack of targeting of active surveillance and largely insufficient sensitivity of passive surveillance. Specific strengths (laboratory diagnostic, information dissemination) were identified, as well as weaknesses some of which are easily correctable (data management, efficien