Recent years have seen tremendous advances in the area of organic electronics mainly motivated by their emerging applications in electronic devices. A very important electronic device that is in the heart of today's microelectronic circuits is the transistor since it represents the building block of all everyday electronics. Very recently, organic based transistors also made their debut in a number of electronic devices and can be arguably viewed as possible alternatives to silicon-based devices in a range of low-cost and high-volume applications.Although recent progress is impressive, use of organic transistors in practical applications is hampered because the minimum requirements (speed, power-dissipation, cost) presently cannot be meet. The proposed work addresses these specific problems using an entirely different approach. We will study the electronic properties of organic semiconductors that are capable of transporting both electrons and holes. These are the so-called ambipolar organic semiconductors. During this fellowship we will develop and advance the knowledge on ambipolar transport in organic semiconductors but we will also exploit and assess various technologically relevant phenomena.We will first study ambipolar transport in a number of known ambipolar organic semiconductors through a combination of electrical, structural, chemical and spectroscopic measurements. Understanding the key electronic properties of these materials is essential for the development of improved or new semiconductors that will be subsequently synthesized through collaborations with various chemistry groups. Using the obtained knowledge, we will demonstrate ambipolar organic transistors and, initially, basic logic circuits like voltage inverters. New applications such as light-emitting transistors and sensors are expected to arise as a result of this work. Moreover, understanding ambipolar transport in organic materials is of basic scientific interest and is expected to benefit other scientific disciplines including chemistry and material science.