3D of BCDs Blue compact dwarf galaxies are low luminosity, compact objects, showing optical spectra similar to those presentes by HII regions. They are metal deficient galaxies with the metallicities of their ionised gas ranging from Z/50 to Z/2. BCDs are gas rich dwarf in which recurrent starburst semm to occur over an older stellar population. In recent years, BCDs have attracted a great deal of interest, as they have been shown to be key objects for solving several astrophysical problems: Characterization of the ongoing star-forming process allows us to study the mechanism that trigger and regulate the star-formation activity in low mass and metal-poor systems. The charcterisation of a possible underlying component is fundamental for understanding how BCDs formed and evolved. The comparison of theirs properties (structural parameters, mean colours and colour gradient) with those characterising other dwarfs (dE, dI, LBS) is crutial for deriving a coherent picture for dwarf galaies in general.