Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an important hematopoietic growth factor and immune modulator. During inflammation, GM-CSF can be secreted by several different cell types, including epithelial cells and leukocytes, and is a critically important cytokine that can drive both innate and adaptive immune responses. GM-CSF assembles and activates its heterodimer receptor complex on the surface of myeloid cells, initiating multiple signalling pathways that control key functions such as cell survival, cell proliferation, and functional activation. Till date, GM-CSF has been studied extensively in murine models and human clinical trials, alone and as adjuvant therapy. This knowledge provides opportunities for the development of new therapies and understands the action of these cytokines in haematological malignancy and chronic inflammation etc.