The local density functional approximation (LDA) is used to calculate magnetic and magneto-elastic properties of itinerant-electron systems at finite temperatures. At the centre of the theory given are spin fluctuations whose modes are coupled by interatomic exchange interactions. The susceptibilities, the Curie temperature, and the thermal expansion coefficients are obtained from a Hamiltonian in which all of the parameters are calculated using ab initio constrained ground-state total energies. Results are given and compared with experiment for three cases having exceptional magneto-elastic properties; these are , the Invar alloy , and .