In the last ten years, humanity has faced new challenges in the field of human and animal health, including emerging viral infections. The widespread occurrence of emerging and re-emerging pathogens (e.g., highly pathogenic avian influenza virus (HPAIV), the new COVID-2019 of zoonotic nature, coronaviruses that cause severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS)) presents a serious threat to humans. Avian pathogens cause devastating economic losses in poultry industries worldwide. Poultry is one of the main sources of protein in Asia. For instance, in China alone, with a population of more than 1.3 billion people, poultry meat consumption has increased to 19.6 kg/year per person (FAO). According to official estimates, this is over 25 million tons per year, or more than 12.7 billion birds. Therefore, poultry farming in Southeast Asia is considered one of the main “vessels” where avian pathogens can evolve. Wild bird migration makes the spread of these pathogens to other regions increasingly likely, as we have seen worldwide with the H5N8 influenza virus. In addition, avian pathogens can cause devastating epizootics among wild birds and threaten the planet’s bioresources. The importance of wild birds as potential vectors of disease has received recent renewed interest, especially in the frame of the global virome/microbiome concept. Understanding the spread of bacterial and viral pathogens in wild birds may serve as a useful model for examining the spread of other disease organisms, both among birds, and from birds to other taxa. This Special Issue aims to summarize recent advances and to attract new research articles that address existing pathogens in poultry and wild birds. It also aims to compare the epidemiological situation across avian pathogens or countries.