In France in 2009, several crop destruction campaigns targeted herbicide-tolerant (HT) sunflowers obtained by mutagenesis. Facing this emerging debate on HT crops, the French Ministries in charge of Agriculture and of Ecology asked INRA and CNRS to gather analytical elements with regard to the real effects, both medium and long-term, of the cultivation of HT crops. This book presents the results of a multidisciplinary expert report on these questions, based on a review of the international literature. HT crops may seem to be useful complementary tools when farmers are facing certain difficult weed-management situations or in the context of a diversification of weed-control strategies. Their repeated use, however, can rapidly induce changes int he weed flora that can constitute more complex challenges in terms of weed control. Issues coming up with the development of agricultural production systems including HT crops are the objects of this expert report: what are the perceptions of these varieties by society and the reasons for the adoption by farmers? Are the savings on herbicides promoted by seed companies long-lasting? Can the cultivation of HT crops impact biodiversity? Overall, this work identifies key points to be taken into account when drawing up guidelines that govern the use of HT crops in order to preserve the effectiveness of this innovation over time. A working group was set up from July 2010 to November 2011, including specialists in ecology, agronomy, herbicide chemistry, genetics, economics, sociology and law. the full report is supported by a bibliographic corpus of more than 1,500 references, assembled by three documentation specialists. it is composed primarily of international peer-reviewed scientific articles, complemented by statistical data, monographs and technical reports. From these references, the experts have extracted, analysed and assembled the relevant elements to clarify the questions at hand.