This work is focused on two major applications of multi–functional materials. In the first one the use of piezoelectric transducers have been studied in order to monitor the health of composite plate–like structures. These transducers can act as signal sources and sensors for guided elastic waves in inspected structures. The excited waves propagating in the material can reflect from various discontinuities such like: boundaries, notches, cracks and delamination. In the next step the time responses registered by the sensors, as inputs for a signal processing algorithm, may be processed to correlate the measured arriving waves with the discontinuities in the structures enabling one to indicate the location of the discontinuities. In the second application the use of shape memory alloy (SMA) components integrated with composite structural elements are investigated. SMA elements in the forms of wires, strips, ribbons, beams, tubes, etc. can be bonded to, or integrated within, various structural elements in order to control their mechanical properties, static as well as dynamic behaviour. This can be obtained thanks to unique effects associated with thermal activation of SMAs leading to significant changes in SMA material properties, which next can also be applied for control purposes. The use of such controllable properties of SMA components in active control of static (deflection) and dynamic (natural frequencies, modes of vibrations, amplitudes of forced vibrations) characteristics of laminated composite beams–like structures have been demonstrated.