At present, substantial amounts of low-cost, fibrous co-products are incorporated into pig diets to reduce the cost of raising swine. However, diets that are rich in fiber are of low nutritive value because pigs cannot degrade dietary fiber. In addition, high-fiber diets have been associated with reduced nutrient utilization and pig performance. However, recent reports are often contradictory and the neg. effects of high-fiber diets are influenced by the fiber source, type, and inclusion level. In addition, the effects of dietary fiber on pig growth and physiol. responses are often confounded by the many anal. methods that are used to measure dietary fiber and its components. Several strategies have been employed to ameliorate the neg. effects associated with the ingestion of high-fiber diets in pigs and to improve the nutritive value of such diets. Exogenous fiber-degrading enzymes are widely used to improve nutrient utilization and pig performance. However, the results of research reports have not been consistent and there is a need to elucidate the mode of action of exogenous enzymes on the metabolic and physiol. responses in pigs that are fed high-fiber diets. On the other hand, dietary fiber is increasingly used as a means of promoting pig gut health and gestating sow welfare. In this review, dietary fiber and its effects on pig nutrition, gut physiol., and sow welfare are discussed. In addition, areas that need further research are suggested to gain more insight into dietary fiber and into the use of exogenous enzymes to improve the utilization of high-fiber diets by pigs.