This thesis aims at providing an overview and analysis of the legal aspects of the participation of more than one person in the commitment of a criminal act. In a situation where several persons participate in the commitment of a criminal act, this is referred to as complicity. It offers an analysis of the various roles of participants in a criminal act, with particular reference to participants in the narrower sense of the term (aiders and abettors). After an elaboration of the term of participant, which points towards the requirements that must be met for a perpetrator to be distinguished from a participant, i.e. the essential differences in the quality of their participation in the commitment of a criminal act, particular emphasis shall be placed on the accessoriness of the aider and abettor in relation to the perpetrator/co-perpetrators, elaborating on the limits of the liability of each participant and the conditions of their culpability. In this, I shall point towards the case law of the Supreme Court of the Republic Croatia, which stresses the importance of delimiting the roles of each participant in the commitment of a criminal act, that is, delimiting their contributions to the commitment of a criminal act, as the legal characterisation of the criminal act that each participant is charged with depends on this contribution.