This paper describes the state of the art in the national doctrine regarding the distinction between primary criminal responsibility (co-authorship) and secondary criminal responsibility (complicity), as legal categories of criminal involvement. To do this, first determine the practical importance of the problem and develops briefly the main theories on the material conception of authorship they have been receptioned the national average, bounded in particular the situation of co-authorship. Then examines the positive regulation, in particular arts. 15 Nº 1-3 and 16 of the Penal Code, taking account of the various doctrinal interpretations about it, ending with a practical example in which the three main models currently in force are articulated: (i) the domain (functional) of fact, (ii ) the analytical theory of the offense and (iii) the quantity theory of criminal involvement