We review current works performed in the field of optical quantum metrology within recent years. The main emphasis is on the analysis of the modern level of theoretical and experimental studies devoted to the generation, transformation and measurement of non-classical states of light, such as N00N-, squeezed and hybrid states of light irradiation. It is shown how they can be useful for improving the measurement accuracy and estimation of unknown phase parameters in both linear and nonlinear metrology. Particular attention is paid to the description of real schemes of quantum metrology, taking into account particle loss, inefficiency of photon detectors, etc. In this regard we establish both the limit (fundamental) constraints imposed by the quantum mechanical uncertainties of the corresponding values in measurement, and the limitations that occur due to the influence of classical noise on the propagation and measurement of the quantized field. A specific place in work is held by the possibilities of quantum metrology based on spontaneous parametrical down conversion of light, that represents irreplaceable instrument of achievement of key results more than 50 years in the quantum optics and the neighbor directions connected with photonics — quantum cryptography, quantum computing and quantum sensorics. In this regard, we analyze the current state of the art of well-known Hong—Ou—Mandel photon anticorrelation effect that explores biphoton interference in various schemes of quantum metrology associated with measurement of temperature, length, material concentration, etc. We also review the usage of biphotons in photometry, radiometry and sensorics for the tasks of absolute calibration of current photon counting detectors, as well as measurements of brightness temperature for hot radiation sources. The phenomena discussed in the review, the methods and approaches of quantum metrology are capable for the latest achievements in the field of quantum radiation sources and detection, and serve important tool in the development and practical implementation of new schemes and algorithms for quantum processing and information transmission.