This review article provides a comprehensive overview of the recent progress in the development of Heusler alloys, particularly Ni-Mn based ones, focusing on their structural crystallinity, order-disorder atoms, phase changes, and magnetic ordering. The crystal structure of these materials is highly dependent on the specific elements comprising the alloy, with high-temperature austenite structures being ordered austenites with a face-centered cubic (FCC) superlattice as an L21 structure or body-centered cubic (BCC) unit cell as a B2 structure. Low-temperature martensite structures can also form as L10, 10M, or 14M martensite structures. The article discusses the influence of temperature and compositional variations on the exhibited phases, as well as the diversification of crystallographic defects affecting their structural and magnetic properties. The ability to regulate valence electron concentration through element substitution is highlighted, along with the challenges and remaining issues in the field. The review also covers the classification of Heusler alloys, including full-Heusler, half-Heusler, and inverse-Heusler alloys, and their respective crystal structures. Additionally, it explores the magneto-structural transition in Ni-Mn-Sn Heusler magnetic shape memory alloys (MSMA), the thermal properties, and the magnetic and shape memory effects of these alloys. The article emphasizes the importance of understanding the structural changes during phase transformations for optimizing MSMA for specific applications.This review article provides a comprehensive overview of the recent progress in the development of Heusler alloys, particularly Ni-Mn based ones, focusing on their structural crystallinity, order-disorder atoms, phase changes, and magnetic ordering. The crystal structure of these materials is highly dependent on the specific elements comprising the alloy, with high-temperature austenite structures being ordered austenites with a face-centered cubic (FCC) superlattice as an L21 structure or body-centered cubic (BCC) unit cell as a B2 structure. Low-temperature martensite structures can also form as L10, 10M, or 14M martensite structures. The article discusses the influence of temperature and compositional variations on the exhibited phases, as well as the diversification of crystallographic defects affecting their structural and magnetic properties. The ability to regulate valence electron concentration through element substitution is highlighted, along with the challenges and remaining issues in the field. The review also covers the classification of Heusler alloys, including full-Heusler, half-Heusler, and inverse-Heusler alloys, and their respective crystal structures. Additionally, it explores the magneto-structural transition in Ni-Mn-Sn Heusler magnetic shape memory alloys (MSMA), the thermal properties, and the magnetic and shape memory effects of these alloys. The article emphasizes the importance of understanding the structural changes during phase transformations for optimizing MSMA for specific applications.