  We have developed a consistent theory of the Heisenberg quantum
antiferromagnet in the disordered phase with a short range antiferromagnetic
order on the basis of the path integral for spin coherent states. We have
presented the Lagrangian of the theory in a form which is explicitly invariant
under rotations and found natural variables in terms of which one can construct
a natural perturbation theory. The short wave spin fluctuations are similar to
those in the spin wave theory and they are of the order of the parameter $1/2s$
where $s$ is the spin magnitude. The long wave spin fluctuations are governed
by the nonlinear sigma model and are of the order of the the parameter 1/N,
where $N$ is the number of field components. We also have shown that the short
wave spin fluctuations must be evaluated accurately and the continuum limit in
time of the path integral must be performed after all summation over the
frequencies $\omega$. In the framework of our approach we have obtained the
response function for the spin fluctuations for all region of the frequency
$\omega$ and the wave vector ${\bf k}$ and have calculated the free energy of
the system. We have also reproduced the known results for the spin correlation
length in the lowest order in 1/N.
