This book undertakes an extensive exploration of manganese-based compounds, such as T�₋ₓSrxMnO₃ (T = La, Pr; x = 0.35, 0.25) using density functional theory and Monte Carlo simulations with a focus on understanding their electronic, magnetic, and magnetocaloric properties. Ba�₋ₓSrxFeO₃ (x = 0, 0.2) is also studied via different approximations, offering a comparative perspective. In addition, the book looks at the influence of magnetism using Monte Carlo simulations, revealing crucial parameters and examining the GdCrO₃ system through DFT and Monte Carlo simulation, shedding light on recent experimental observations. Additionally, Monte Carlo studies investigate magnetic and magnetocaloric features of Sr₂FeMoO₆, La₂SrMn₂O₇ bilayer manganite, perovskite ferromagnetic thin films surface effects, and SmFe�₋ₓMnxO₃ perovskite. In essence, this book significantly advances our comprehension of magnetic and magnetocaloric phenomena across diverse materials and is well-suited for both experimentalists and computational researchers working in this field.