This study looks at the impact of the legal system on agrobiodiversity (or agricultural biodiversity) – the diversity of agricultural species, varieties and ecosystems – and at the implementation of farmers' rights in Brazil. The first part of the study discusses the origins of agriculture and the different farming systems in the world, and the history of agriculture in Brazil, from the pre-Columbian period through modern times, highlighting the diversity of agricultural systems. Using an interdisciplinary approach, it takes up the (emerging) concept of agrobiodiversity and its interfaces with food security, nutrition, health, environmental sustainability, climate change and agro-fuels. After these initial concepts are presented, the study analyzes the impacts on agrobiodiversity of the following legal instruments: the Seeds Law, the International Convention for the Protection of New Varieties of Plants, the Plant Breeders’ Rights Law, the Convention on Biological Diversity, the International Treaty on Plant Genetic Resources for Food and Agriculture and Provisional Measure 2186-16/2001 (on access to genetic resources). It concludes with a discussion on the forms of implementation of farmers’ rights in Brazil, on the laws already adopted in other countries and regions (India, Africa, European Union, Italy and Switzerland), on the interfaces between the free software movement, the “commons” movement and seeds, as well as the legal instruments to protect cultural heritage and their application in farming systems, protected areas and geographical indications.