The work presented in this Ph.D. thesis is mostly related to the measurement and interpretation of the cross-correlation of different tracers. This is achieved using spectroscopic data from the BOSS survey. These tracers include the MgII absorbers, the Damped Lyα Systems (DLA), the Lyα forest, the quasars and the galaxies. Save the last mentioned, all tracers are measured from quasar spectra from BOSS. The galaxies are taken from the BOSS CMASS catalogue. The first cross-correlation addressed is that of Mg II absorbers with CMASS galaxies. A new method for measuring the equivalent width of metal absorbers is presented and it is applied to the absorption doublet. The method is followed by a series of tests to verify its behaviour. These tests also show that previous measurements might not be detecting the weakest absorbers. Therefore, they might be biased. This method allows for a measurement of the cross-correlation of weaker metals that are not strong enough to be catalogued. Then, the cross-correlation between the DLAs and the Ly forest is considered. Since the Lyα forest autocorrelation has already been studied (see e.g. Delubac et al. 2015; Blomqvist et al. 2015), the Lyα parameters are well constrained. Those constraints are used to provide more accurate measurements of the DLA bias when analysing the cross-correlation of DLAs with the Lyα forest. A new estimator for the cross-correlation, originally developed by Nicolás Busca for the analysis of the Lyα autocorrelation and later adapted to the measurement of the cross-correlation, is presented. Finally, the cross-correlation of quasars with the Lyα forest is also measured, focusing on the small scales effects. We show that a contamination from metals is clearly present in the cross-correlation. Also, some of the possible non-linear effects are discussed. A model for the effects of the quasar radiation on the surrounding IGM is presented. This model relates the average lifetime of a quasar with an asymmetry observed in the cross-correlation of quasars and the Lyα forest.