This book contains the papers presented at a Nato Advanced Re search Workshop entitled "DENITRIFICATION IN THE N-CYCLE," held in Braunschweig (W-Germany) from 24 to 27 Mai 1983. All expenses were provided by the North Atlantic Treaty Organization. The scientific programme was in the first instance planned by some members of the Eco-Science Panel under the stimulating organization of Dr. Oscar Ravera and the final programme was prepared in co-operation between Ravera and myself. However, even during the meeting important con tributions were added. The meeting was hosted by the Microbiologi cal Dept. of F.A.L., which also took care of the organizatory as pects. Nitrate is constantly lost from both terrestial and aquatic ecosystems, causing rnixed feelings between ecologists and agricul turists. While bacteriologically very rnuch is known, the ecology of the processes is still poorly understood, nor can it be evaluated what it rneans as an econornic loss for farrners and world food produc tion. Therefore this NATO Advanced Workshop was established to per mit a lirnited nurnber of scientists active in this field to corne to gether for a short while to address the following objectives: 1) To exchange ideas between scientists (bacteriologists and ecologists) and agronornists. 2) To assess the state of the art. 3) To discuss the difficulties of experimentation in the field. 4) To define future research. In order to accornplish these objectives, the workshopwas organ ized in three parts with the following thernes: 1) Bacteriological aspects of dentrification