  The paper presents the short review of our to-day knowledge of vacuum
condensates in QCD. The condensates are defined as vacuum averages of the
operators which arise due to nonperturbative effects. The important role of
condensates in determination of physical properties of hadrons and of their
low-energy interactions in QCD is underlined. The special value of quark
condensate, connected with the existence of baryon masses is mentioned. Vacuum
condensates induced by external fields are discussed. QCD at low energy is
checked on the basis of the data on hadronic tau-decay. In the theoretical
analysis the terms of perturbation theory (PT) up to alpha^3_s are accounted,
in the operator product expansion (OPE) - those up to dimension 8. The total
probability of the decay tau->hadrons (with zero strangeness) and of the
tau-decay structure functions are best described at alpha_s(m^2_tau) =
0.330+-0.025. It is shown that the Borel sum rules for tau-decay structure
functions along the rays in the q^2-complex plane are in agreement with the
experiment with the accuracy ~2% at the values of the Borel parameter |M^2|>
0.8 GeV^2. The magnitudes of dimensions 6 and 8 condensates were found and the
limitations on gluonic condensates were obtained. The sum rules for the charmed
quark vector currents polarization operator was analysed in 3 loops (i.e., in
order alpha^2_s). The value of charmed quark mass (in MS-bar regularization
scheme) was found to be: m_c(m_c) = 1.275+-0.015 GeV and the value of gluonic
condensate was estimated: <(alpha_s/pi)G^2> = 0.009+-0.007 GeV^4. The general
conclusion is: QCD described by PT + OPE is in a good agreement with experiment
at Q^2 >~ 1 GeV^2.
