This chapter reviews the International Criminal Court Appeals Chamber’s guidance on preliminary issues that affect the functioning of the Court. These issues include the interpretation of the Rome Statute, the weight and emphasis to be given to the sources of law and the role of different actors within the Court. It also notes that the Appeals Chamber has utilised articles 31 and 32 of the Vienna Convention of the Law of Treaties to interpret the Rome Statute, analysed article 21 (1) (a) – (c) of the Rome Statute on the applicable law and interpreted the Regulations of the Court. It also notes that the importance of the travaux preparatoires has been emphasised by the Appeals Chamber but observes that the weight to be given to the jurisprudence of other international criminal tribunals is far more complex. It then goes on to elucidate how the Appeals Chamber has adjudicated on the exercise of judicial functions by the Appeals Chamber, the role of the Registrar and the Registrar’s relationship with Chambers, the authority of the Prosecutor regarding investigations as well as the role played by defence counsel, duty counsel and other forms of representation.