Over the last decade, several multi-wavelength studies have demonstrated the 
existence of tight correlations between the collective number and luminosity 
of bright X-ray binaries, as well as the hot interstellar medium (ISM), and 
the star formation activity of the late-type host galaxies.These properties 
are valid both in the local Universe and at intermediate redshifts, making 
X-ray observations a powerful tool to estimate the star formation rate in 
distant galaxies. Recent results show that the multiple-galaxy-wide average 
relations for bright X-ray binaries also hold on small, sub-galactic, scales. 
On much larger scales, X-rays from star-forming galaxies in the early Universe 
(z > 15) regulate the thermal history of the intergalactic medium (IGM) and 
leave an imprint on the 21 cm signal, determining its amplitude. The IGM 
temperature fluctuations caused by soft X-rays from hot ISM are large 
compared with that due to X-ray binaries with harder spectra.