Agroforestry is a land use system in which trees and shrubs grow alongside food crops and/or animals. It’s a dynamic ecological system that diversifies and sustains production for increased economic, social, and environmental benefits. Agroforestry has been practised for a very long time in many places. Different systems include: improved fallows, taungya, home gardens, alley cropping, growing multipurpose trees or shrubs on farmlands, boundary planting, farm woodlots, orchards, tree plantations, shelterbelts, windbreaks, conservation hedges, fodder banks, live fences, apiculture, and silvopastoral systems.
Learn more about agroforestry and its benefits in this toolkit from the UN Food and Agriculture Organization. http://www.fao.org/sustainable-forest-management/toolbox/modules/agroforestry/basic-knowledge/en/ 
In these videos, learn more about different agroforestry systems: http://www.fao.org/sustainable-forest-management/toolbox/modules/agroforestry/tools/en/ 
In this video, learn more about conservation farming with natural vegetative strips: http://www.fao.org/sustainable-forest-management/toolbox/tools/tool-detail/en/c/422550/ 
The World Agroforestry Centre has many resources on agroforestry, including:
What is Agroforestry: http://www.worldagroforestry.org/about/agroforestry  and
Success stories: http://www.worldagroforestry.org/output?field_type_tid=2897 
Photo credit: Ton Rulkens at https://flickr.com/photos/47108884@N07/14678137749