We review atomistic spin model studies, a new approach for theoretical investigations, on magnetic properties of permanent magnets. In the atomistic modeling, the microscopic details of magnetic
parameters and lattice structures are realistically considered, and the temperature effect, including thermal fluctuation, is properly treated based on statistical physics methods: Monte Caro methods and
stochastic Landau– Lifshitz–Gilbert equation methods. We introduce how to treat thermal effects for static and dynamical properties using these methods. Focusing especially on neodymium permanent
magnets, we discuss features of magnetization, domain wall, coercivity of a grain, nucleation and pinning fields, and dysprosium substitution effect, which were first elucidated with those methods.