This book constitutes the proceedings of the 4th International Conference on Nano-Networks, Nano-Net 2009, held in Lucerne, Switherland, in October 2009. The 36 invited and regular papers address the whole spectrum of Nano-Networks and spans topis like modeling, simulation, statdards, architectural aspects, novel information and graph theory aspects, device physics and interconnects, nanorobotics as well as nano-biological systems. The volume also contains the workshop on Nano-Bio-Sensing Paradigms as well as the workshop on Brain Inspired Interconnects and Circuits.Nano-Net 2009 Full Papers and Invited Papers.- The Impact of Persistence Length on the Communication Efficiency of Microtubules and CNTs.- Single and Multiple-Access Channel Capacity in Molecular Nanonetworks.- Timing Information Rates for Active Transport Molecular Communication.- Information Transfer through Calcium Signaling.- Quantitative Analysis of the Feedback of the Robust Signaling Pathway Network of Myosin V Molecular Motors on GluR1 of AMPA in Neurons: A Networking Approach for Controlling Nanobiomachines.- RF Control of Biological Systems: Applications to Wireless Sensor Networks.- Sub-micrometer Network Fabrication for Bacterial Carriers and Electrical Signal Transmission.- Pulse-Density Modulation with an Ensemble of Single-Electron Circuits Employing Neuronal Heterogeneity to Achieve High Temporal Resolution.- Carbon Nanotube Nanorelays with Pass-Transistor for FPGA Routing Devices.- Quantum-Like Computations Using Coupled Nano-scale Oscillators.- Optimization of Nanoelectronic Systems Reliability by Reducing Logic Depth.- Coherent Polarization Transfer through Sub-wavelength Hole Arrays.- Study on Electrical and Optical Properties of the Hybrid Nanocrystalline TiO2 and Conjugated Polymer Thin Films.- Through Silicon Via-Based Grid for Thermal Control in 3D Chips.- Can SG-FET Replace FET in Sleep Mode Circuits?.- Functional Model of Carbon Nanotube Programmable Resistors for Hybrid Nano/CMlcÎ