Assessing and reducing the seismic risks associated with historical structures require an appropriate knowledge of structural behaviour and characteristics, as suggested by recent national and international guidelines concerning cultural heritage. However, historical structures are characterised by a high level of uncertainty, which affects material properties and structural schemes and is related to deterioration processes or previous interventions and structural modifications. The level of knowledge can be increased by experimentally evaluating a structure's dynamic properties, and the resultant data can be used to refine and update numerical models that are representative of the real structural behaviour. Moreover, the periodic monitoring of relevant parameters can help identify eventual deterioration phenomena. Thus, dynamic tests, in conjunction with model updating, are becoming reliable tools for non-destructively assessing historical structures. In this article, a brief discussion of the basic principles of dynamic identification under operational conditions is presented. Two tests with historical structures are then presented, and the main results are reported. The high performance of operational modal analysis techniques and the interesting opportunities these techniques provide for the structural assessment of historical structures are discussed.