The primary objective of research scientists working in the field of rumen function is to advance animal production through greater understanding of the mechanisms involved in digestion and metabolism in the rumen. This article covers some of the more recent developments in the field together with some ideas on meeting the challenge of advancing Animal Science. Recent research on energy metabolism covers mechanisms of energy generation in anaerobes and their influence on the efficiency of the ruminal fermentation. Factors affecting microbial protein synthesis and the extent to which dietary protein leaves the rumen undegraded (bypass protein) and which are critical for the efficient use of dietary N are reviewed. Factors limiting digestion of plant material, treatment of low quality roughages to improve digestibility and the use of solid substrate fermentors are discussed. The nutritional dependence of ruminants on their microflora makes them especially suited to genetic manipulation of the rumen ecosystem. Ideas on the genetic modification of rumen bacteria are covered. The importance of technology and methodology in the advancement of science is discussed briefly together with a few examples of recent advances in analytical instrumentation.