The study of the relationships between agriculture and biodiversity is important to sustain biodiversity for the future. The landscape level has an influence, which has been until now mainly related to the importance of semi-natural elements. But in agricultural areas crop land is often dominant and acts on biodiversity by the resources it provides and the effects of disturbances induced by agricultural practices. The mosaic of crops is ephemeral and highly dynamic in space and time according to farming practices and crop rotations. The aim of this chapter is to assess the role of agricultural landscape heterogeneity on biodiversity. Landscape heterogeneity may be measured from different perspectives, considering non-cropped areas versus crop ones, or taking into consideration the dynamics of the mosaic of crops and agricultural practices. From studies on a long term ecological research site in Brittany, France, we present how these different approaches of landscape heterogeneity allow a better understanding of the diversity of processes driving biodiversity in agricultural landscapes. Most of all we underline the necessity to include knowledge of farming systems and farming practices in the analyses.