Rotor and control design are two of the most challenging tasks during the development of an autonomous micro helicopter. Both areas are strongly affected by the extremely small size of the vehicle.The rotors are working in the low Reynolds numbers reducing efficiency and limiting the autonomy time of the helicopter. On the control side the small size leads to faster system dynamics and limits the payload for accurate sensors and actuators. These challenges and how to address them are the main topics of this book.In order to increase rotor efficiency, the influence of various blade parameters, lift enhancing devices and the drive train is investigated. The control problem is addressed by developing a nonlinear model for the coaxial helicopter muFly. In order to find the system parameters an identification process is carried out. Finally, the control strategy is presented including both high-level and low-level aspects.Altogether, this book serves as a guideline for other researchers and engineers who aim to develop an autonomous micro helicopter the size and mass of a small bird.