This chapter commences a case study analysis into the influence of economic and financial conditions on the operation of public finance law and the constitutional distribution of authority between parliaments and executive governments. The fiscal activities (taxing and spending) of the central governments of the UK and the Commonwealth of Australian between 2005 and 2016 are selected for analysis. The chapter begins with a detailed examination of appropriation and taxation legislation in the two jurisdictions, including the respective financing contribution of annual and standing statutes and their role in delegating authority to treasury departments. The chapter then examines the influence of expansions and contractions in economic output on the balance of constitutional authority possessed by parliaments, with a special focus on the impact of the financial crisis. Thereafter, the often-hidden reality of public spending in breach of appropriation legislation is studied, along with the legal frameworks governing public accounts and audit. The chapter concludes by observing the vast amount of fiscal authority delegated to treasury departments by public finance law.