All meat has been grass. This statement of the old Greeks is still valid and thus plants contribute to the needs of a growing world popula­ tion. Their other key role for human life is reflected by their photosynthetic activity. Intensive agriculture reduces the carbon diox­ ide content of the atmosphere. The improvements of cultivated plants towards stable yields and desired quality characteristics are the sub­ jects of plant breeding. Here, an introductory picture of the present state of this topic in research and application is given. The senior author, H. Kuckuck, wrote the first edition in 1939 as a small German booklet, hence the nickname little cuckoo (Kuckuck = Engl. cuckoo). During the last 6 years (the fifth German edition appeared in 1985) again numerous results of basic research have found practical application, making extensive additions neces­ sary. Further, it seemed timely to change to the international language of science: English. For help in translation we are grateful to Silke Kluth and Kathy Seaman. Since agricultural sciences - like all others - have become more specialized, we were happy to welcome D. Baringer (Sect. 5.4), W. Hondelmann (Sects. 4.4, 4.5, and 6), V. Stoy (Sect. 4.2), and T. Thtlioglu (Sects. 2.3.1.4 and 3.5) as contributors to this edition. Finally, we would like to thank Springer-Verlag for all their efforts in helping to transform a small German booklet into a book available to a wider audience.