Phagocytosis, which belongs to a type of endocytosis, is an active transport for exogenous materials entering cells. It relates to the fundamental process of nutrition uptake, bacteria or pathogen defense, and cell death in various cell types, such as macrophages, dendritic cells, osteoclasts, and epithelial cells. These specialized cells express receptors that activate the transduction signals, resulting in phagocytosis to maintain cell function and homeostasis. Thus, the cell membrane receptor and signaling can also affect many cell types. For instance, the phagocytosis of neurons and synapses essentially affects neuron innervation. The phagocytic capacity of antigen-presenting cells, such as dendritic cells, is vital to immunity. Phagocytosis plays a crucial role in programmed cell death by engulfing apoptotic bodies. It's essential to note that defects in phagocytosis can lead to serious health concerns, including neutropenia and respiratory burst disorder. In this book, different topics related to phagocytosis will be discussed, including nutrition uptake, cell death, bacteria or pathogen invasions, immune response, disease associated with phagocytosis problems, and the dynamic changes of cell membrane, cytoskeletons, and protein signals in phagocytosis process. The current overviews of phagocytosis will be presented here.