  We study finite temperature ($T$) properties of the continuum quantum field
theory of systems with a ferromagnetic ground state. A scaling theory of the
$T=0$ system is discussed carefully, and its consequences for crossovers
between different finite $T$ regimes in dimensions 1, 2, and 3 are described.
The results are compared with recent NMR measurements of the magnetization of a
quantum Hall system with filling factor $\nu=1$; we predict that the relaxation
rate $1/T_1$ of this system may have a finite $T$ ``ferromagnetic coherence
peak''.
