The last decade has witnessed an impressive progress in the quality of organic field-effect transistors (FETs) based on conjugated polymers and molecules. This progress has mainly resulted from the investigation of organic materials used to fabricate thin-film devices, and has led to drastic improvements in their chemical purity and structural quality. Despite this remarkable progress on the material side, our basic understanding of the physics of organic FETs –i.e. of the microscopic processes determining and limiting the FET performance- has not advanced at an equal pace. The lack of fundamental understanding is now posing concrete problems that are hampering the development of better and faster organic transistors needed for future applications. To address this issue, an increasing number of research groups are now investigating organic transistors based on single crystals of conjugated molecules, exhibiting unprecedented quality and reproducibility. In this talk, I will first motivate with a few examples why single-crystal transistors are crucially important for the study of the intrinsic electronic properties of organic FETs. I will then discuss the basic technology needed to work with single crystalline transistors and show that they indeed provide experimental access to the intrinsic device characteristics. In the second part of the talk, I will focus on some of the microscopic electronic processes that determine the transport properties of dielectric/organic and metal/organic interfaces. I will show that we are starting to gain quantitative understanding of these processes and I will illustrate the relevance of this understanding for applications.Alberto Morpurgo is a condensed matter physicist, with a broad interest in the electronic properties of materials and devices. After receiving a Master in Physics from the University of Genova (Italy), he moved first to the Scuola Normale in Pisa and then to the University of Groningen (the Netherlands), where he did experimental work on mesoscopic physics and received a PhD degree in 1998. In 1998-99, Dr. Morpurgo was postdoctoral fellow at Stanford University, working on carbon nanotubes. At the end of 1999, he moved back to the Netherlands, Delft University, where he is currently associate professor. In Delft, Dr. Morpurgo has extended his work on mesoscopic physics to a variety of systems (two-dimensional electron gases, carbon nanotubes, metal-superconductor structures, and, more recently, graphene). In parallel, he developed a research line on the investigation of organic field-effect transistors based on the use of single-crystals of molecules. Dr. Morpurgo is the recipient of the Midema price 2000 for the best Dutch PhD thesis on condensed matter physics during the period 1998-99. He also is a NWO VIDI(2000) and VICI(2006) Laureate.