Feed efficiency in dairy cattle is moderately heritable and selection for its improvement theoretically would be effective. Despite this, direct selection for feed efficiency is not practiced in dairy cattle. Growth of milk recording programs which monitor feeding information has made selection for feed efficiency, or at least efficiency of concentrate conversion, possible on a large scale. However, it has been estimated that correlated response to direct selection for increased milk yield probably results in 70–95% of the potential improvement in feed efficiency that could be achieved through direct selection for feed efficiency. Current selection practices for increased body size may be detrimental to feed efficiency. In swine also, little direct selection for improved feed efficiency is practiced. Experimental studies for selection for feed efficiency have been less successful than expected. Correlated response from selection for an index that combines growth rate and backfat seems to be as effective in improving feed efficiency as direct selection. Development of automated feeding devices which allow measurement of individual feed intake under group penning will facilitate monitoring of and selection for improved feed efficiency. Key words: Selection, feed efficiency, swine, dairy cattle