In this work we give a schematic description of the observational features of the solar corona at different wavelengths, also in the light of recent observations performed by the coronal instruments aboard the SOHO spacecraft, whose diagnostic capabilitites are summarized. The typical event dynamics is characterized in the time-altitude domain in order to provide an indicative reference to the time and space resolution requirements for diagnostic techniques. Different 2-D coronal electron density models for the quiet as well as the perturbed corona are discussed as fundamental tools in physical modelling. Typical coronal diagnostics based on radio observations is considered, such as the derivation of the coronal density and the magnetic field strength; solar radio events are characterized in the time-altitude domain as coronal tracers and advanced radio imaging diagnostics is reviewed, which allows the 3-D reconstruction of coronal structures. We finally mention the diagnostics based on propagative effects of radio waves and stress the limit on the maximum achievable space resolution imposed by coronal scattering processes to high frequency imaging observations.