**4. Reconciling Cosmological Indicators to GRBs**

After the first part of this review, in which we faced the main properties of GRBs, their possible theoretical background and progenitors, we are now in a condition to relate our understanding directly to cosmology. In fact, for cosmological purposes, it is essential to get the distance of astronomical objects and thus the use of GRBs would help in computing such distances up to very large redshifts. In particular, source physical parameters mostly depend on luminosity and size and then cosmic bounds can be inferred if there exists a relation between distances and redshifts. This prerogative is intimately related to two distinct concepts, i.e., distance indicators<sup>17</sup> and standard candles<sup>18</sup> .

Below, we elucidate the main properties of such objects and the most important consequences they have in observational cosmology.
