||The detection of a significant fraction of the highest redshift quasars (z > 5) in the (sub-)mm wavelength range indicates that a substantial amount of dust has been synthesized already during the first billion year since the Big Bang. Recent 24 micron observations with Spitzer have shown that very hot dust is present close to the QSO core in most z >5 quasars. However, both the (sub-)mm and MIR observations can only catch tails of the dust emission spectrum, at lambda_rest > 200 m, and at lambda_rest < 5 m, respectively. Measuring the peak of the dust emission, expected to reach 10 .. 30 mJy around lambda_rest ~ 50 m (120m < lambda_obs < 700m), has been beyond the capabilities of FIR satellites or ground-based sub-mm telescopes. Thus, critical properties, such as FIR luminosity, dust temperatures and mass, remain unconstrained. To improve on this situation, we propose a Herschel Guaranteed Time Key Programme (GT KP) to collect far-infrared and sub-millimeter photometry of more than 100 high redshift quasars using the PACS and SPIRE instruments. We plan to determine the SEDs of three samples of QSOs: (i) all z > 5 quasars known to date, (ii) a dozen radio loud quasars and galaxies at the highest redshifts, and (iii) 29 Broad Absorption Line (BAL) quasars together with a comparison sample of 17 non-BAL QSOs at matching redshifts. In addition, we plan to obtain PACS spectroscopy of four very dust-rich and lensed high-redshift QSOs and galaxies for spectral line diagnostics, which will help to disentangle the contributions of AGN- and starburst-heated dust and thus complement the SED-based study. We will spend in total 165 hours of PACS GT in this key programme, 115 hours for the photometry with PACS and SPIRE, and 50 hours for the FIR spectroscopy.