The sources relating to the tithe pose many problems, but sometimes, as argued in this book, they constitute the best documentary base available to approach the movement of agricultural products in many Spanish and European regions in modern times. The historian must calibrate the margin of error that his estimates entail and the advantages and disadvantages related to the use of tithes with respect to other alternative approaches to the trajectory of crops in the modern age. The almost complete abandonment of the use of decimal sources has not been a success. In this work, some proposals are made to select and exploit this documentation to improve our knowledge of agricultural growth in modern Spain. The texts correspond to the papers presented by the different authors at the Study Day on "The Tithe as a Source for Rural History", held on October 26, 2018 in Girona.