Flexible structures are one of the most frequently used elements in different systems. They can be easily shaped to any desired form, they are light-weight, relatively inexpensive, and they have the required mechanical properties for many applications. In many cases, implementation of these systems requires real-time (active) application of a force or a moment to guarantee the required performance. Also sometimes, real-time measurement of the deflections in these systems is needed to measure a property or a parameter. To address these needs, flexible structures have been taken to a different level by enhancing them with smart materials. One of the most frequently used smart materials for flexible structures are piezoelectric layers. The result is a smart flexible structure which can provide a measurement of its deflections, and/or its displacement can be actively controlled. Active control of smart structures is one of the most important topics in this field. Using active control, a desired level of vibration can be induced in the structure, or undesired vibration can be eliminated. Additionally, deflection measurement in flexible smart structures can be improved alongside current developments in other sensing devices. To this end in this dissertation, several new control techniques have been proposed for active vibration control of flexible smart structures based on the method of positive feedback, in addition to decentralized measurement and control using novel networked-based consensus techniques. The methodologies developed in this dissertation are listed as: • Multimode Modified Positive Position Feedback • Modified Positive Velocity Feedback • Hybrid Positive Feedback • Spatial Modified Positive Position Feedback • Multi Positive Feedback • Nonlinear Modified Positive Position Feedback • Nonlinear Integral Resonant Controller • Nonlinear Integral Positive Position Feedback • Optimal consensus observer design for piezo-active smart structures • Consensus-based multi-piezoelectric microcantilever sensor • Leader-follower based consensus vibration controller • Consensus Positive Position Feedback The mentioned approaches which are designed for sensing and control of smart flexible structures are numerically and/or experimentally investigated, and their strengths and weaknesses in each case are thoroughly discussed. This dissertation provides a useful reference for engineers who seek to implement smart structures, and inspires them to develop and apply novel techniques in this field.