At present biogas plants produce biogas mainly from slurry by liquid fermentation. But the low substrate digestation of herbaceous biomass by liquid fermentation permits to use only a low amount of herbaceous biomass. Since April 2007 the collaborative project entitled “Development of a combined dry-wet fermentation process to produce biogas from herbaceous biomass substrates” is conducted at the Laboratory for Integrated Energy Systems of the University of Applied Sciences in Stralsund. The combined dry-wet fermentation is a progressive fermentation process that shall lead to a better substrate digestion, as well as to a higher biogas production.