In swine management we have the opportunity to determine the social groupings of our animals. We determine which pigs are in the same pen, and which pigs are not. This process will be referred to as sorting. With increasing farm size, more pigs may be selected from in order to form a group, allowing the implementation of very effective sorting strategies. Within the industry there is a general consensus that sorting is important in order to achieve maximum productivity. However, in a more intensive production system there are many situations where a sorting strategy may not apply. Historical systems in which pigs were limit fed on the floor were subject to dominance related problems. Sorting by weight is a means of reducing dominance related variation in production. This practice will be effective if resources (such as feed) are limited and easily defendable. Such conditions exist in groups of gestating sows if they are not individually fed. Grower-finisher pigs are generally fed ad libitum and do not benefit from sorting by weight. Restricted space allowances do not lend themselves to defence, and so all pigs experience a reduction in growth within crowded pens. Sorting on the basis of nutritional needs can be effective, and leads to sorting grower-finisher pigs by sex, and newly-weaned pigs by size in order to provide the best diets to each group.