As in the UK there are normally monthly stamp releases in Germany. Stamps are issued via Deutsche Post. However, it is very rare for Deutsche Post to release a specific set of stamps in one month which is the tradition in the UK. For example, in the UK there may be a William Shakespeare set of stamps released or a Thomas The Tank Engine set of stamps released comprising of between 4 and 10 stamps. In Germany random stamps are issued on a monthly basis. For example, recently two stamps were released relating to modern german life, one stamp was released relating to the Hamburg tunnel and one stamp was released relating to children going to aquariums. However, over a period of time a series of stamps relating to one subject may be released. For example, over a two year period a set of stamps was released picturing lighthouses. More recently there has been a set of stamps showing planets and stars in the solar system.
Whereas The Royal Mail only keeps its stamps in circulation for a year, Deutsche Post sell their stamps until the issue has been sold out. It is still possible to buy stamps from 2006 for example!
Germans also use stamps as a way of giving money to charity. You will frequently see a stamp that says 55c+25c. This is a 55c stamp with 25c going to charity and will cost 80c to buy from a post office in Germany.