Trickling filters are biofilm reactors that provide energy-efficient removal of COD and Ammonia. The possible application in wastewater treatment should always be checked. The German experiences with trickling filters are presented, and the new design guideline will be explained. In Germany, the first Trickling Filter was built at the WWTP Stahnsdorf near Berlin in 1906. Actually, about 300 wastewater treatment plants are equipped with Trickling Filters. Concerning COD removal, they provide quite low outlet values (45 mg/l) and the median COD-elimination was calculated by 90%. Trickling Filters have a lower specific electricity consumption on average than other wastewater treatment processes in Germany. The chapter explains the new German design standard of the DWA A 281 (Design of trickling filter plants, plants with rotating disc and submerged fixed beds. Bemessung von Tropfkörperanlagen, Anlagen mit Rotationstauchkörpern und Anlagen mit getauchten Festbetten, 2020 [1]), which is based on the fractioning of the COD. It gives hints on how to calculate the inlet loads and flow, and how to select the carrier material. It includes the design of the pre-treatment and of final clarifier. For the calculation of the Trickling Filter volume, it provides the degradation ratios for COD and NH4-N. Also, some new developments for Trickling Filters, e.g., the combination with biological P-Removal, are shown. Decentralized Trickling Filters with greywater can cool down the inlet temperature of an air conditioning unit, which will be presented. How to handle malfunctions in Trickling Filter systems is presented, and countermeasures are described. Finally, the influence of the temperature is also investigated, and the performance of a highly loaded trickling filter in the potato industry is discussed. The chapter shows the status and future applications of the trickling filter in Germany.